76 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



the testicles were entirely non-functional can not be maintained, for 

 the cells of Sertoli, the interstitial cells, and spermatocytes may have 

 been present. These may exercise some normal functions. A cyto- 

 logical study will be undertaken later. The | wild females were fertile 

 and also equal to the guinea-pig in size. Therefore, the | wild 9f both 

 sexes average the same as the guinea-pig, and the peculiar sterility of 

 the males has no effect, similar to that reported by Geddes. The 

 sterile J wild males are actually smaller than the guinea-pig. 



The difference between these sterile males and those in Geddes's 

 experiments is that, in the former, the testicles were present and may 

 have functioned in secreting hormones; whereas in the latter case they 

 were really entirely non-functional. That the testes of sterile male 

 hybrids were partially functional we are quite certain, for the secondary 

 sexual characters were all present. The prostate glands and seminal 

 vesicles were perfectly well developed. Sixteen hybrids were castrated 

 at the age of 3 weeks, for the sake of comparison. Their seminal vesicles 

 were greatly atrophied and they showed no sexual instinct throughout 

 Ufe. All these facts lead us to believe that the steriUty of the male 

 hybrids is not comiparable at all to that sterility due to pathological 

 conditions, kryptorchism, and castration. It is not surprising then, 

 that the long bones of the sterile | wild male hybrids and the male 

 guinea-pigs were of equal length. 



ANOMALIES OCCURRING IN THE HYBRIDS. 



In addition to the frequent occurrence of the interparietal bone, 

 peculiar to the hybrids, there were a number of other anomalies which 

 should be mentioned. 



(1) The wild C. rufescens and the guinea-pig have 4 toes on the 

 front feet and 3 on the hind feet. By selection, Castle (1906) was 

 able to produce a race of guinea-pigs having 4 toes on the hind feet. 

 There occurred among the | wild a male (cf 202) with 6 well-developed 

 functional toes on the left front foot and left hind foot. Like most 

 males of this blood, he was sterile. The anomaly was never repeated. 

 This may have been a reversion to the ancestral pentadactylous con- 

 dition, brought about by recombining factors. It is interesting to note 

 that the extra toes occurred on the left side, for Castle found that the 

 extra toe in his polydactylous race was more frequent on the left side 

 also. 



(2) There occurred some monstrosities in the hybrids which I have 

 never seen in guinea-pigs, although many hundreds have been care- 

 fully studied. In one of the hybrids the first cervical vertebra, the 

 atlas, was completely fused with the skull. In another hybrid both 

 scapulae were bent so as to form a sharp angle, whereas normally they 

 should be flat. In two female hybrids (9 263 and 9 393) the clitoris 



