SEASONAL MODIFICATIONS IN TESTES OF 

 VERTEBRATES 



By R. ? M. OSLUND 



University of Illinois 



THERE is an obvious relation- 

 ship between the phenomena of 

 sexual urge and of testicular 

 activity. That the testis aug- 

 ments the mating instinct has long been 

 known, and the literature contains a great 

 deal of controversy concerning which of 

 the testicular elements wields this 

 influence. 



In most animals there are seasonal 

 variations in the size of the testis and in 

 the relative quantity of its constituent 

 elements. These changes are found in all 

 animals that mate but once each year. 

 In hibernating animals the changes appear 

 to be more pronounced than in the non- 

 hibernating forms. Where the seasonal 

 changes in sexual behavior and in testicu- 

 lar structure are marked it is reasonable to 

 expect that any parallelism between 

 testicular modification and physiological 

 action might be seen. Such a parallelism 

 might be found between sex activity and 

 (i) volume of a particular tissue or (z) cell 

 proliferation or (3) cytological appear- 

 ance. Each of these parallelisms has been 

 reported as existing. 



It has been difficult to ascertain the 

 importance of any change in any of the 

 tissue substances of the testis, partly 

 because of the scarcity of studied material. 

 This is true because most of the reports 

 found in the literature are based upon 

 observations covering only a few months 

 of the year. A second difficulty has been 



due to the fact that in many reports the 

 exact time of mating has not been noted. 

 The failure to take into consideration the 

 exact time of breeding rather than the 

 approximate time of the year has caused 

 much of the confusion and difference of: 

 opinions. Perhaps the greatest difficulty 

 in studying the physiology of the testis 

 has been caused by the fact that some 

 writers have attempted to prove a theory 

 with their facts instead of forming a 

 theory to explain the observed facts. 

 As a result, the literature contains many 

 contradictory statements that are difficult 

 to interpret. 



In this review an attempt has been made 

 to glean the facts from the literature upon 

 seasonal changes in vertebrate testes and 

 to present these facts in as clear a manner 

 as possible. In order to do this the 

 literature on the seasonal changes in each 

 group of animals is reviewed separately 

 and an attempt is made to evaluate these 

 observations. The recorded observations 

 are then discussed and interpreted with 

 reference to the known facts regarding the 

 time and peculiarities of sexual activities 

 of these animals. 



MODIFICATIONS IN THE TESTES OF FISH 



Fish testes are made up of lobules con- 

 taining cysts of germ cells. These lobules 

 correspond to the spermatogenic tubules 

 of mammals and empty into longitudinal 

 collecting ducts which in turn open into 



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