FERTILITY OF PARENT SPECIES AND HYBRIDS. 81 



ings, and the like did not prevent the wild females from breeding. The 

 wild males, as previously stated, could only be mated to tame females 

 with difficulty; and yet, when successful matings were secured, these 

 tame females bore the usual average per litter characteristic of the 

 guinea-pig. This shows that the wild males produced an abundance 

 of spermatozoa and fertilized the usual number of eggs, exactly the 

 same as a tame male would have done. 



A study of the fecundity of the wild, tame, and hybrid females will 

 show whether or not we are justified in concluding that environment 

 has played little or no part. No attempt is being made to underrate 

 the effect of environment upon fertility, for it is recognized that nutri- 

 tion, age, change of surroundings, temperature, drugs, disease, and the 

 like may exercise profound effects. However, since the wild breed in 

 captivity and the wild males are fertile in crosses with guinea-pigs, 

 captivity itself may be eliminated as a factor causing sterility in the 

 less wild hybrid sons. The original wild male (cfl) lived and bred 

 in captivity from 1903 to 1908 — a period of almost 5 years. The great 

 difficulty with these wild in captivity was not that their wildness pre- 

 vented fertility, but that their nervous, excitable disposition made them 

 difficult to handle and led to injuries in one way or another. Nehring 

 experienced little or no trouble with wild C. aperea in captivity and 

 they remained fertile at the same time. 



We do not know what the exact fertility of the wild C. rufescens 

 may be in its native habitat, nor have we any basis upon which to 

 compare its fertility in the wild state with its fertility in the laboratory 

 pens. There are some observations by naturalists upon the fertility 

 of C. aperea in the wild state, but they are meager and contradictory. 

 Nehring found that this species was more prolific in captivity than it 

 was reported to be in the wild state. The wild C. rufescens, which were 

 bred in captivity, aborted their young in a few cases. Abortion is, of 

 course, not infrequent in the domestic guinea-pig, but I am inclined to 

 believe that these abortions were more frequent in the wild cavy. The 

 abortions may possibly be supposed to indicate a degree of disturbance 

 in the sexual functions and signify a tendency toward sterility. If this 

 is true it is the only evidence of any lessened fertility in the wild 

 due to captivity. The abortions ceased in the hybrid females, and 

 there were no other signs of any sexual disturbances in the later, more 

 dilute wild hybrids, other than the sterile males previously mentioned. 

 The pure wild were very easily frightened, and when disturbed would 

 run about frantically. It is not impossible that the abortions were 

 caused by these violent paroxysms of fear and the subsequent effects 

 on foetal nutrition and other functions. 



The fertility of the other parent species, the tame guinea.-pig, is well 

 known. Under the excellent conditions of housing, food, and care in 

 our laboratory, a sterile guinea-pig is very uncommon. Of all males 



