SEASONAL MODIFICATIONS IN TESTES OF VERTEBRATES 



*55 



the epididymis and vas deferens. During 

 the non-spermatogenic season these 

 lobules are small and contain only a few 

 germ cells. All cells in any one lobule are 

 of one stage of development, the testis 

 in this respect resembling that of arthro- 

 poda. As spermatogenesis progresses 

 these lobules become filled with germ cells, 

 and as the number and size of the cells 

 increase the lobules become enlarged. 

 This continues durirg multiplication and 

 growth of spermatogonia and spermato- 

 cytes and perhaps during the early part of 

 the spermatid period. Thereafter the 

 size of the individual cells decreases with- 

 out any augmentation in their number and 

 the lobules thereupon decrease in size 

 proportionately. When the sperm are 

 ejected the lobules are emptied and sud- 

 denly decrease in volume. 



Between the lobules are found con- 

 nective tissue, blood and lymph vessels, 

 and nerves. When the lobules are dis- 

 tended with spermatogenic tissue they 

 press tightly against each other. The 

 cells of the connective tissue lying between 

 them then resemble typical connective 

 tissue cells. When the lobules decrease 

 in volume, during the spermatid and 

 spermatozoa stages and especially when 

 the spermatozoa are ejected, some of the 

 connective tissue cells enlarge and become 

 somewhat modified in structure. These 

 cells are commonly referred to as inter- 

 stitial cells and some authors maintain 

 that they are glandular cells. 



The entire mass of tissue between the 

 lobules in fishes and amphibia and the 

 tissue between the tubules in birds and 

 mammals should be designated inter- 

 tubular tissue, while the term interstitial 

 tissue should include only the modified 

 connective tissue cells. This distinction 

 is necessary since an increase in the space 

 between the tubules, intertubular space, does 

 not always imply an increase in inter- 

 stitial tissue. In a review of the literature 



this distinction is difficult to maintain 

 since most writers have failed to note the 

 differences, but the fact should not be 

 overlooked in evaluating the reports. 



Size of the testis in fish largely depends 

 upon the size of the lobules. When the 

 lobules enlarge the testis increases in 

 volume. When the lobules shrink follow- 

 ing sperm ejection the testicular volume 

 does not proportionately decrease because 

 of change in intertubular tissue, especially 

 because of the interstitial cell increase in 

 the case of fishes. Later, as the inter- 

 stitial cells decrease in quantity, the testis 

 further shrinks in volume. 



Temperature of the water, abundance of 

 food, and to some extent the amount of 

 light are prime factors in the life of the 

 fish. Anatomic and physiological sea- 

 sonal modifications are especially influenced 

 by changes in temperature. For example, 

 if a female about to deposit her eggs is 

 placed in very cold water, egg deposition 

 may be delayed indefinitely. 



In Yellow Perch (Perca flavesans') Turner 

 (36) reports that the volume of the testis 

 is greatest during late November. He 

 also states that the maximum size is in 

 January. His data indicate that the 

 greatest weight is in November. The 

 volume increase at this time is very rapid 

 because of the increase in the number of 

 germ cells in the lobules. The large size 

 of the testis persists until early March 

 and then suddenly falls when spawning 

 takes place due to ejection of ripe sperm. 

 This decrease continues from early March 

 to late May. The beginning of increase 

 in volume precedes the decline in tem- 

 perature and is due to the early stages of 

 spermatogenesis. The first spermatozoa 

 are formed in the early part of September 

 and are present in the lobules until their 

 expulsion takes place the following spring. 

 No data were given concerning the 

 intertubular tissue. 



Seasonal variations in the size of the 



QUAE. REV. BIOL., VOL. Ill, NO. 2 



