114 CARL R. MOORE. 



with the opposite testis normal ; obviously the testis at fault has 

 never descended from the abdomen. In the guinea pig descent 

 of the testis occurs before or immediately after birth, and in 

 order to reproduce as nearly as possible congenitial abdominal 

 retention, the animal must be operated very soon after birth. 

 Guinea pig testes from five days to twenty days after birth 

 (sometimes later) show but little tendency to differentiate into 

 the elements of the germ cell line and usually spermatozoa are 

 not found in the seminiferous tubules until from forty to sixty 

 days of age. Operation can, therefore, be delayed until the 

 animal has become quite self-supporting and the testis confined 

 to the abdomen considerably in advance of tubular differentia- 

 tion ; with such procedures we are able, therefore, to reproduce 

 essentially the conditions of congenitial retention. 



The question of single or bilateral elevation of the young 

 testis was definitely solved by our earlier experiments. It was 

 pointed out that an abdominally confined, prepubertal testis 

 reacted differently if its partner was normal or if it were either 

 removed or likewise confined in the abdomen. When one testis 

 is carrying on its normal gametogenetic activity a prepubertal 

 testis in the abdomen remains essentially in an embryonic resting 

 condition for months and even years; the seminiferous tubules 

 retain essentially the same diameter, the cells do not perceptibly 

 change their embryonic character, the interstitial spaces remain 

 in fundamentally the same condition as at the time of elevation 

 and the testis as a whole does not increase in size. If, however, 

 both prepubertal testes of an animal are elevated to the abdomen, 

 or if one is so elevated and the opposite testis removed, then 

 the reactions are of a different character. The abdominal testis 

 does usually increase in size, and the tubules in their diameter, 

 but such an increase is essentially due to an edematous condition 

 of the testis as a whole; the cells of the seminiferous tubules 

 instead of retaining the embryonic condition become differenti- 

 ated into cells believed to be Sertoli cells; the interstitial spaces 

 are often much larger than the embryonic type and usually 

 contain numerous and conspicuous cells of Leydig. This type 

 of testis is not an embryonic type, but one that has undergone 

 considerable modification. It is apparently very definitely 



