DURATION OF TESTIS ACTIVITY OF STURNUS VULGARIS IN RELATION TO TYPE OF ILLUMINATION 1

Transcription

1 VOL. IX, No. 4 OCTOBER, 1932 DURATION OF TESTIS ACTIVITY OF STURNUS VULGARIS IN RELATION TO TYPE OF ILLUMINATION 1 BY THOMAS HUME BISSONNETTE AND ARTHUR PEHR ROBERT WADLUND. (Trinity College, Hartford, Connecticut.) (Received 12th April, 1932.) (With Two Plates and One Text-figure.) INTRODUCTION. A STUDY of the normal regressive changes in the testes of starlings (Sturnus vulgaris), in Hartford, Connecticut, showed that these glands decrease in size and in spermatogenic activity in the latter part of May and early June, while the periods of daylight are still increasing in daily duration and intensity. Spermatozoa disappear from the testes earlier in some birds than in others; but are invariably absent before June 15th (Bissonnette, 1930 b). Later experimental work showed that increasing daily periods and intensity of light, containing a relatively large amount of red rays, were factors which affected the onset and acceleration of spermatogenesis in these birds (Bissonnette, 1931 a, b, 1932 a, b; Bissonnette and Wadlund, 1931), while green light of similar intensity proved inhibitory to spermatogenesis. Possible causes of this early regression and loss of spermatogenic activity are, among others: (1) the relative increase of ultra-violet with the beginning of summer may be injurious and cause regression before the summer solstice; (2) a relative increase in the green rays of light received by the birds, from reflection by grass and green foliage in May and June, may cause regression and necrosis of germ-cell elements before June 21st; (3) complete spermatogenesis itself may involve or induce such changes in the birds, in a certain time, that sexual maturity cannot be maintained beyond a period (which probably varies with different birds, with different exposures to light, and with different previous sexual conditions) even while all the environmental factors necessary for spermatogenesis are at or near the optimum level. In other words, products of sexual activity may accumulate beyond a threshold level and thereby throw the reproductive mechanism out of gear. 1 "Studies on the Sexual Cycle in Birds; No. VIII." Aided by grants from the Committee for Research in Problems of Sex and the Committee for Grants-in-Aid of the National Research Council of the U.S.A. for , administered by T. H. Bissonnette. Facilities for study were also received from the School of Agriculture and the Laboratory of Experimental Zoology of the University of Cambridge. For all of these aids the authors are very grateful. JHB'IXIV 22

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4 342 T. H. BISSONNETTE and A. P. R. WAD>LUND The experiments to be described below were carried out to test the first and last of the above-mentioned possibilities. Previous studies showed that red light of 1-7 foot-candles intensity induces the appearance of metamorphosing spermatozoa in about 23 days, in December and January (Bissonnette and Wadlund, 1931). It was therefore of interest to compare the effects of red light of this intensity with those of the same red light in combination with light from an electric bulb designed to give the luminous and heat equivalent of midsummer mid-day sunlight, including the ultra-violet component. The available lamp which most nearly approached this was a General Electric Company's "sunlamp." A photographic analysis of its spectrum is given by the company in its prospectus. METHOD. As in previous studies from this laboratory, experimental light treatments with artificial light were added to a period of daylight each day. In this case the periods were added to a constant daily daylight period of 9^ hours, obtained by curtaining the large windows from 4.30 p.m. till 7.00 a.m. daily (Bissonnette and Wadlund, I93 1 )- On January 20th, 1931, 105 birds, of both sexes and both juvenile and mature (having passed at least one season of sexual maturity), were brought into the laboratory and distributed indiscriminately as to sex and age, birds to a cage. They were fed and cared for as described elsewhere (Bissonnette, 1932 i; Bissonnette and Wadlund, 1931). To one cage (" red-light" cage), red light of 1-7 foot-candles intensity of illumination was delivered at the roost (Bissonnette and Wadlund, 1931). To another (" red-sunlamp " cage), was delivered red light of the same intensity and also light from the "sunlamp" mentioned above, acting at about 3 ft. from the roost, laterally. Birds in the other cages were kept as controls. The daily daylight periods of all birds were shortened, when the experiment began on January 24th, by about 18 min. per day from the normally increasing period of that time of year, and the intensity of daylight reaching the birds during the day was somewhat reduced by keeping the birds in the laboratory where the light was less intense than outside. These changes must be taken into account in comparing red-light effects induced in this experiment with those obtained in the previous experiments (Bissonnette and Wadlund, 1931). They account for a lag in onset of progressive testis changes in some birds and for regression in controls, particularly in those birds furthest from the windows. From January 24th, throughout the experiment, curtains were pulled from 4.30 p.m. till 7.00 a.m., and the lights turned on by a time switch in the experimental cages for 6 hours per night. Birds from the two experimental cages and from one or other of the control cages were killed as samples on February nth, 18th, 25th and March 25th, at 18, 25, 32 and 60 days. After March 25th, no more birds were left in the "red-

5 Duration of Testis Activity of Sturnus vulgaris 343 sunlamp " cage. Three birds, two males and one female, were left in the "red-light" cage and continued at the same light ration till April 22nd, when they were killed, after 88 days of treatment. The technique of preparation and the measurement of the testes after removal were the same as those described by Bissonnette and Wadlund (1931). Photomicrographs were made in like manner. Data concerning these birds' testes are given in Table I. Graphs showing the changes in average volume of both testes throughout the time of the experiments, for "controls," "red-light" birds, and "red-sunlamp" birds, are shown in Fig. 25. The numbers from each group killed at any one time are small (1-4), and in some cases the spread of variation between birds from the same lot is very great; hence these averages are subject to great probable errors. They show, however, the general trend of volume changes. Where the spread is great, the maximum and minimum testis volumes for the lot are given, so there need be no misunderstanding as to the real nature of the figures used and the import of the graphs. EFFECTS OF TREATMENTS. After 18 days, the controls (Figs. 1, 2) and "red-light" birds (Figs. 3, 4, 5, 6) had undergone some regression as a result of the initial 18 min. reduction in daily daylight. However, some of the "red-light" birds had recovered from the initial reaction and had undergone germ-cell multiplication with the appearance of synizesis stages (Figs. 5, 6). Others were slower to recover and start spermatogenesis; possibly because they roosted habitually farther from the light source than did those responding more quickly. On the other hand, "red-sunlamp " birds showed no signs of regression or delay of activation, but rather accelerated spermatogenesis with metamorphosing spermatozoa, within the 18 days (Figs. 7, 8), the shortest time in which such stages have been induced by experimental light treatments. After 25 days, on February 18th, the controls (Fig. 9) had undergone further regression toward the midwinter condition, and the minimum testis volume. The testes of the "red-light" birds had reacted unequally as before, but all showed very great acceleration of activity over the controls. The stages reached varied from the first appearance of synizesis stages (Fig. 10) to rhetamorphosing spermatozoa (Fig. 11). The testes of " red-sunlamp " birds had, in some cases, reached complete spermatogenesis (Fig. 12), and in other cases showed the production of immature spermatozoa (Fig. 7). The stage of spermatogenesis was still far in advance of that of the "red-light" birds. After 32 days, on February 25th, the testes of the control birds (Figs. 13, 14) had increased in size and showed an advancement of germ-cell activity, as compared with controls after 25 days. This may have been due to an exposure to more intense light in a cage nearer to the windows than was the case before. However, they were still smaller in average size than those of control birds after 18 days. The testes

6 344 T. H. BISSONNETTE and A. P. R. WADLUND of the "red-light" birds (Figs. 15, 16) had produced mature spermatozoa but had not yet reached their maximum size. They were still enlarging, while the testes HO - DAY 8 X-..x-»"controls." 0 Q "red-light" birds. = "red-sunlamp" birds. Fig. 25. Graph of average volumes of both testes per bird under the three types of treatment, taking as unity the average volume of both testes of " control" birds after 18 days of treatment. N.B. The numbers of birds from each cage killed at each time are small and the variations in size are great. Where the " spread " between largest and smallest testes of any lot is great, the sizes of the greatest and of the smallest testes of the lot are shown in the graph. The graph gives only a very rough idea of the curves of volume changes (Table I). 100 of the "red-sunlamp" birds had reached almost the maximum size and a state of complete spermatogenesis (Fig. 17). After 60 days, on March 25th, the testes of control birds were again smaller (Fig. 18), and the amount of cytoplasm and numbers of germ cells within the

7 Duration of Testis Activity of Sturnus vulgaris 345 tubules were less. The testes of "red-light" birds (Fig. 19) had nearly reached the maximum size in some cases and a stage of complete spermatogenesis. The testes of the " red-sunlamp " birds (Figs. 20, 21, 22) had passed the climax of spermatogenesis and of testis size and showed all the conditions of regression attained in nature between June 15th and August 3rd (Bissonnette, 1930 b). In nature, this occurs after about 175 days of increasing daily light. These birds maintained approximately complete spermatogenesis under experimental conditions for about half as long as do birds in nature (Bissonnette and Chapnick, 1930; Bissonnette, 1930 b), and within about 60 days they were induced to pass through phases of the sexual cycle which in nature require about 142 days (January 24th to June 15th). So far as can be determined by histological examination, the changes in these testes under extreme artificial stimulation are the same as occur normally in nature, except in respect to the rate at which the changes are effected. In both cases, the rates of attainment of any stage in the cycle differ somewhat in different birds. One of these birds (Fig. 22) had lost only spermatozoa and secondary spermatocytes, but had retained a few primary spermatocytes and numerous synizesis stages. It had lagged behind the others. Very probably the whole cycle of this bird had been slow, and it was, therefore, late in reaching and passing the climax. The testes of all the birds examined, from this lot, at this particular time, had decreased in size and activity; while those of "red-light" birds were only approaching the condition of maximum activity and size. After 88 days, on April 22nd, the testes of the "red-light" birds had passed the crest of activity and size (Figs. 23, 24), though the testes of some birds still showed mature spermatozoa in the tubules (Fig. 24), while others had regressed to a condition somewhat similar to that of the least regressed testes of the "redsunlamp " birds after 60 days (Figs. 22, 23). All the testes had decreased in size and activity (Fig. 25). The testes of "red-light" birds were slower to reach their maximum size and activity, but continued to produce spermatozoa for a longer period than did those of the " red-sunlamp " birds which had received much stronger light. The differences were such as to suggest that differences in the intensity of illumination (rather than a specific action of the ultra-violet content of the "sunlamp") caused the observed differences in various phases of the cycle. Both sets of birds failed to maintain either complete spermatogenesis or anything approximating maximum size (Fig. 25). DISCUSSION. It is suggested that regression under stimulating intensities of light is due neither to ultra-violet light (either in nature or under experimental conditions) nor to the increase in the green content of the light which reaches the birds when the amount of green foliage increases in spring; but is more likely due to a failure of the sex mechanism to maintain a high rate of germ-cell multiplication and maturation beyond a definite period, which varies with different birds and with different exposures to light, which induce different rates of acceleration of germ-cell activity.

8 346 T. H. BISSONNETTE and A. P. R. WADLUND The more stimulating the effect of the illumination, the more quickly is the mechanism thrown out of gear. The more slowly sexual maturity is induced by light stimulation, the longer a high degree of reproductive activity is maintained. In other words, the duration of any part of the sexual cycle bears an inverse relationship to the strength of the stimulus which induces spermatogenic activity. This stimulus has been shown to vary with the daily period, intensity, and colour, or wave-length, of the light received by these birds (Bissonnette, 1930 a, 1931 a, b, 1932 ft; Bissonnette and Wadlund, 1931). The rays in the visible part of the spectrum and particularly those of the longer wave-lengths are the most effective stimulants. Certain alternatives suggest themselves as explanations for these phenomena. Among others are the following: (1) cessation of activity may be due to the development of a tolerance for the light used (cf. Loeb and Friedman, 1931, for tolerance to pituitary extract); (2) it may be due to a type of "trigger" reaction, which releases the spermatogenic tension or sets in motion a train of regressive reactions, emanating, not primarily from the gonads themselves, but, more probably, from the anterior lobe of the hypophysis and/or other endocrine glands (stimulated to activity in excess of the optimum for sex activity and damaging to gametogenesis in either testis or ovary). The apparent likelihood of the second alternative, and of the anterior lobe of the hypophysis as, at least, one of the other glands intimately related to the whole reproductive activation or cycle, increases as studies of the interrelationships between the gonads and the anterior lobe of the hypophysis become more complete. This study does not show any marked effect of ultra-violet rays as such upon the sexual cycle in starlings. The reactions of the testes to light containing ultraviolet do not differ in any essential features from those induced by light of similar intensity but which lacks the ultra-violet component. The differences of reaction above described are merely those of time and rate of incidence, and can be accounted for rationally by differences in intensity of incident light [in conformity with our previous findings (Bissonnette, 1931 a, b)], or by a greater content of the red rays (Bissonnette and Wadlund, 1931; Bissonnette, 19326). This is being studied further. If the ultra-violet content of the "sunlamp " spectrum is inhibitory in effect, it is not sufficiently so to counteract appreciably the effects of increased intensity of illumination, or of the doubled amount of red light used, and so reduce the acceleration of spermatogenesis. It can hardly be, therefore, the sole cause of early regression in June. Even red light, known to be very stimulating, was unable to maintain maximum testis activity for 56 days (Fig. 25). Testis regression, following a period of complete spermatogenesis, which occurs on an increasing exposure to light in nature (Bissonnette, 1930 b), also occurs under artificial light stimulation in the laboratory, when the birds are exposed to red light (the most stimulating type of light so far used). It is immaterial whether artificial midsummer mid-day sunlight, with its content of ultra-violet, is used in conjunction with the red rays. It may be possible that the constancy of the light stimulus which was used in these experiments was a factor which affected the process of regression;

9 Duration of Testis Activity of Sturnus vulgaris 347 but in nature the light is increasing when the regression sets in, in early June (Bissonnette, 1930 b). Red light is effective in stimulating testis activity in these birds, unless they are already at their maximum activity. If the onset of regression is due to developing light tolerance, or to a "release" of regressive reaction trains (probably in the anterior lobe of the hypophysis, as suggested above), the reaction of the sexual cycle of the starling to light may have many elements in common with the recurrent cycles in polyoestrous animals. The inability to maintain complete functional activity may be due either to an exhaustion of substances elaborated by such a gland as the anterior lobe of the hypophysis, to their neutralisation by substances from the active gonads, or to an inhibition of the anterior lobe by the gonad hormones, reducing its output of gonad-stimulating substances, permitting the gonads to go out of action from lack of the stimulator (Martins, 1931; Martins and Rocha, 1931); or, as appears likely, certain anterior lobe hormones may become too concentrated for gonad activity and injure the germ cells, the regression of which leads to a reciprocal effect on, and inhibition of, anterior lobe activity (Bellerby, 1928; Domm, 1931; Biingeler and Ehrhardt, 1931; Hartman and Squier, 1931; Wiesner and Marshall, 1931; and many others). The results of much study of the gonad-hypophysis relation to sexual cycles of many species, chiefly mammals, suggest that the anterior lobe of the hypophysis is the endocrine gland most concerned with sexual cycles in many Amphibia, birds and mammals. The great similarity of the results obtained from transplants of the anterior lobe, or from injections of extracts from it, in birds and mammals to those resulting from light treatments, similar to those used in these experiments, suggests that the light treatments act through the stimulation of the anterior lobe to activity and that this increased activity induces the observed modifications of the sexual cycles (Bissonnette, 1930 a, 1931 a, b, 1932 a, b, c; Bissonnette and Wadlund, 1931; Baker and Ranson, 1932; Hill and Parkes, 19300,6, 1931; Domm, 1931; Schockaert, 1931; Engle, 1931a, b; Hisaw, Fevold and Leonard, 1931; Moore, 1931; Moore and Price, 1931; Evans and Simpson, 1930; Adams, 19310,6; Burns and Buyse, 1931 a, b; Buyse and Burns, 1931; Claus, 1931; Noble and Richards, 1930; Noether, 1930; Morash and Gibbs, 1929; Smith, 1930, 1931; Smith and Engle, 1929; Riddle, 1931 a, b; Riddle and Flemion, 1928; Riddle and Polhemus, 1931; Wolfe and Cleveland, 1931; Hill, 1931; and many others). Many specific differences in the gonad-hypophysis relation and in susceptibility to anterior lobe therapy have already been brought to light for Amphibia and other animals, and variations in susceptibility to light treatments as between birds and mammals have also appeared (Adams, 1931 b; Bissonnette, 1932 c, and as previously cited). Evidence has also been obtained that the activity of the anterior lobe varies with different stages of the reproductive cycle (Smith and Engle, 1929). Diet also influences the reproductive cycles in many animals (Agduhr, 1931 a, b; Baker and Ranson, for voles, private communication; and some unpublished data on starlings on a restricted diet, cited in Bissonnette, 1932 d), and in many cases the effects are correlated with changes in the anterior lobe of the hypophysis, as well as in the gonads.

10 348 T. H. BISSONNETTE and A. P. R. WADLUND More recent studies on adrenalectomy in rats indicate the influence of these glands on oestrus and sexual cycles through an adrenal-hypophysis relationship (Martin, 1932). It is, therefore, still an open question as to whether the light treatments act through the hypophysis-gonad mechanism or through an adrenalhypophysis-gonad series of interactions. This problem is being studied further. SUMMARY. 1. Between January 24th and April 22nd, 32 male starlings, with females, were subjected to (a) no added light (controls), (b) 1-7 foot candles of filtered red light together with the total light from a General Electric Company's "sunlamp" at about 3 ft. distance, approximating to midsummer mid-day sunlight, and (c) 1-7 foot candles of filtered red light, after dark for 6 hours, in addition to a gl hours constant daily daylight period (about 18 min. reduction from the daylight period in nature at the beginning of the experiment). 2. Samples from (a), (b) and (c) groups were killed for study after 18, 25, 32 and 60 days, and from (c) group also at 88 days. 3. Testes of controls (a) underwent a slight regression, remained smaller than at the first killing, and did not increase in germ-cell or other gonadal activity. 4. Testes of birds in (c) group were slower to reach their maximum size and spermatogenesis (60 days) than were those from (b) group (32 days), with their more intense light and approximately double the amount of red rays. Both sets of birds failed to maintain their maximum size and spermatogenesis, though the more slowly reacting (c) group maintained it longer than did the (b) group. 5. The reaction differences are such as to indicate that differences in light intensity and amount of red rays caused the observed differences in relative length of the phases of the sexual cycle and, particularly, in the length of periods of maximum testis size and activity rather than any specific action of ultra-violet rays or excess of green light. 6. Even on the highly stimulating exposures to light used, the duration of maximum spermatogenic activity was limited and varied with different birds, with different exposures to light, and with different types of light, and the consequent rates of germ-cell activity. The duration of any phase of the sexual cycle bore an inverse relation to the effectiveness of the stimulating exposure to light, which, in turn, depended on the daily period, intensity, wave-length and rate of change of illumination. 7. Alternative modes of causation of these phenomena and the probable mediation of the anterior lobe of the hypophysis in the reactions are discussed. REFERENCES. ADAMS, A. E. (1931 a). Proc. 2nd Intern. Congr.for Sex Research, pp London. (1931 A). Proc. Soc. Exp. Biol. and Med. 28, AGDUHR, E (1931a). Proc. 2nd Intern. Congr.for Sex Research, pp London. (1931 b). Proc. 2nd Intern. Congr.for Sex Research, pp

11 Duration of Testis Activity of Sturnus vulgaris 349 BAKER, J. R. and RANSON, R. M. (1932). Proc. Roy. Soc. B, 110; in press. BELLERBY, C. W. (1928). Lancet, i, BISSONNETTE, T. H. (1930 a). Amer. Journ. Anat. 45, (1930 b). Amer. Journ. Anat. 46, (1931 a). Journ. Exp. Zool. 58, (1931 b). Phytiol. Zool. 4 (4), (1932 a). Science, 74, (1932 b). Pkytiol. Zool. 5 (1), (1932 c). PTOC. Roy. Soc. B, 110; in press. (1932 d). Nature; in press. BISSONNETTE, T. H. and CHAPNICK, M. H. (1930). Amer. Journ. Anat. 45, BISSONNETTE, T. H. and WADLUND, A. P. R. (1931). Journ. Morph. 52 (2), BCNGELBR, W. and EHHHARDT, K. (1931). Klin. Wtchr. 10, 593-5, cited from Phyttol. Abstr. 16 (6-7), 419. BURNS, R. K. Jr. and BUYSE, A. (1931 a). Anat. Rec. 48, supplement, p. 12. (1931 b). Anat. Rec. 61 (2), BUYSE, A. and BURNS, R. K. Jr. (1931). Proc. Soc. Exp. Biol. and Med. 29 (1), 80. CLAUS, P. E. (193I). Phytiol. Zool. 4, DOMM, L. V. (1931). Proc. Soc. Exp. Biol. and Med. 29 (3), ENGLE, E. T. (1931 a). Anat. Rec. 48, supplement, p. 17. (1931 b). Endocrinology, 15 (3), EVANS, H. M. and SIMPSON, M. E. (1930). Anat. Rec. 45, 215. HARTMAN, C. G. and SQUIER, R. D. (1931). Anat. Rec. 50 (3), HILL, M. (193I). Sci. Progr. (London), 25 (99), HILL, M. and PARSES, A. S. (1930 a). Journ. Phytiol. 69, xvm, xix. (1930 b). Journ. Phytiol. 69, xxiii, xxiv. (1931). Proc. Roy. Soc. B, 107, HISAW, F. L., FEVOLD, H. L. and LEONARD, S. L. (1931). Proc. Soc. Exp. Biol. Med. 29, LOHB, L. and FRIEDMAN, H. (193 I). Proc. Soc. Exp. Biol. Med. 29, MARTIN, S. J. (1932). Amer. Journ. Phyttol. 100 (1), MARTINS, T. (1931). CJi. Soe. Biol. Paris, 106, 510-n. MARTINS, T. and ROCHA, A. (1931). Endocrinology, 15 (5), MOORE, C. R. (1931). Proc. 2nd Intern. Congr.for Sex Research, pp London. MOORE, C. R. and PRICE, D. (1931). Amer. Journ. Physiol. 99, MORASH, R. and GIBBS, O. S. (1929). Journ. Pharmacol, and Exp. Ther. 37 (4), , cited from Biol. Abttr. 5, NOBLE, G. K. and RICHARDS, L. B. (1930). Amer. Mus. Nov. 396, 1-3. NOETHER, P. (1930). Arch. Exp. path. u. Pharmak. 150 (5-6), , cited from Biol. Abttr. 6 (8-9), RIDDLE, O. (1931 a). Phytiol. Rev. 11 (1), (1931 b). Amer. Journ. Phyttol. 97 (4), RIDDLE, O. and FLEMION, F. (1928). Amer. Journ. Phytiol. 87 (1), RIDDLE, O. and POLHEMUS, I. (1931). Amer. Journ. Physiol. 98 (1), SCHOCKAERT, J. A. (1931). Anat. Rec. 50 (4), SMITH, P. E. (1930). Amer. Journ. Anat. 45 (2), (*93i)- Journ. Amer. Med. Ass. 97 (25), i86t-3. SMITH, P. E. and ENGLE, E. T. (1929). Anat. Rec. 42, 38. WEBSNER, B. P. and MARSHALL, P. G. (1931). Quart. Journ. Exp. Phytiol. 21 (2), WOLFE, J. M. and CLEVELAND, R. (1931). Anat. Rec. 51 (2),

12 35 T. H. BISSONNETTE and A. P. R. WADLUND EXPLANATION OF PLATES. N.B. Figs are photomicrographs of comparable testis sections taken in the first instance at 335 diameters and reduced in reproduction to about 225 diameters. Where two or more sections show no differences appreciable at the reduced magnification, only one section is figured; other testes which resemble the one figured are listed, marked with a ( ). PLATE I. Fig. 1. Mature "control" bird after 18 days, January 24th-February nth, C 1. Fig. 2. Mature "control" bird after 18 days, January 24th February nth, C 2. Fig. 3. Mature "red-light" bird after 18 days, January 24th February nth, C 3. Fig. 4. Mature "red-light" bird after 18 days, January 24th February nth, C 4. Fig. 5. Mature "red-light" bird after 18 days, January 24th-February nth, C 5. Fig. 6. Young "red-light" bird after 18 days, January 24th February nth, C 6. Fig. 7. Two mature " red-sunlamp" birds after 18 days, January 24th February nth, C 7; and at 25 days, January 24th-February i8th, C 15*. Fig. 8. Two young "red-sunlamp" birds after 18 days, January 24th February nth, C 8, C 9*. Fig. 9. Young "control" bird after 25 days, January 24th February 18th, C 10; mature "control" bird after 25 days, January 24th February 18th, C n #. Fig. 10. Mature "red-light" bird after 25 days, January 24th February 18th, C 12. Fig. ir. Mature "red-light" bird after 25 days, January 24th February 18th, C 13. Fig. 12. Young "red-sunlamp" bird after 25 days, January 24th February 18th, C 14. Fig. 13. Two mature "control" birds after 32 days, January 24th February 25th, C 17, C 16*. PLATE II. Fig. 14. Young "control" bird after 32 days, January 24th-February 25th, C 18 Fig. 15. Mature "red-light" bird after 32 days, January 24th-February 25th, C 19. Fig. 16. Mature "red-light" bird after 32 days, January 24th-February 25th, C 20. Fig. 17. Mature and young "red-sunlamp" birds after 32 days, January 24th-February 25th, C 21 and C 22 #, respectively, and mature "red-light" bird after 60 days, January 24th March 25th, C 26*. Fig. 18. Mature and young "control" birds after 60 days, January 24th March 25th, C 24 and C 25*, respectively. Fig. 19. Mature "red-light" bird after 60 days, January 24th-March 25th, C 25. Fig. 20. Young "red-sunlamp" birds after 60 days, January 24th-March 25th, C 27. Fig. 21. Two mature " red-sunlamp " birds after 60 days, January 24th-March 25th, C 29 and C 28*. Fig. 22. Mature "red-sunlamp" bird after 60 days, January 24th-March 25th, C 30. Fig. 23. Mature "red-light" bird after 88 days, January 24th-April 22nd, C 31. Fig. 24. Mature "red-light" bird after 88 days, January 24th April 22nd, C 32.

13 JOURNAL OF EXPERIMENTAL BIOLOGY, IX, 4, PLATE I. < I BISSONNETTE AND WADLUND DURATION OF TESTIS ACTIVITY OF STURNUS VULGARIS IN RELATION TO TYPE OF ILLUMINATION (PP ).

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15 JOURNAL OF EXPERIMENTAL BIOLOGY, IX, 4. PLATE II. BISSONNETTE AND WADLUND DURATION OF TESTIS ACTIVITY OF STURNUS VULGARIS IN RELATION TO TYPE OF ILLUMINATION PP )-

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