47O L. V. DOMM AND MARY JUHN. 



identical weight, that valid conclusions cannot be drawn from 

 the data obtained in different cocks. The tables compiled are 

 omitted for this reason. 



Where testes of one pair were observed as was done for the 

 control cockerels (Tables 1 1. -IV.) the left testes were larger than 

 the right in one case out of two at twenty-four weeks. At 

 thirty-two weeks, the left testes were larger in two out of three 

 pairs, while at forty-eight weeks, the left testis was very slightly 

 heavier (o.oi per cent.) than the right one in one pair; it was 

 smaller than the right testis in two pairs and finally there was 

 one pair in which the gonad weighed exactly the same amount 

 on the left and on the right side. 



The tendency of the left testis to be rather larger than the 

 right one in embryonic chicks has been observed by a number of 

 authors. Firket, '14 (4), states that the right testis is noticeably 

 smaller than the left one in the chick at the seventh day of 

 incubation and quotes Semon, '87 (5), as saying that the left 

 testis is much larger at the beginning of its development. 



According to Swift, '16 (6), the left embryonic testis is notice- 

 ably larger than the right one in the five day chick and the 

 germinal epithelium of the left gonad is also thicker and more 

 extensive. This difference in favor of the left testis is also 

 visible in the six and nine day chick. Riddle, '16 (7), finds no 

 difference between the right and the left testes in common fowl, 

 the age of the birds is not stated. 



The greater tendency towards hypertrophy of the left testis 

 discussed under 1 1. a, is presumably associated with this embry- 

 onic condition, and is of interest in comparison with the very 

 pronounced asymmetry of the female. 



IV. DISCUSSION. 



From the results described in the preceding pages as well as 

 from the experimental data published by Benoit, the occurrence 

 of compensatory hypertrophy following unilateral castration in 

 young male fowls seems to be well established. We found 

 compensatory hypertrophy of the retained gonad also in adult 

 cocks, differing in this point from Benoit's observations. The 

 period during which the surviving testes were permitted to 



