10 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



impregnated by the larger-sized guinea-pig male. The matings were 

 obtained with much difficulty, for the wild sire at first harassed and 

 bit the tame females almost beyond recognition; but, by keeping him 

 in solitary confinement for some time, and then placing him with a 

 female which had just given birth to young, copulation was success- 

 fully brought about. The young appeared in due time (63 to 67 days) 

 and in the usual guinea-pig number, showing that such wild males, 

 producing an abundance of sperm, are wholly fertile with tame females. 

 Our stock of tame females used as the mothers of the hybrids con- 

 sisted of large healthy animals of known color varieties (except the 

 dams in two cases of young not used in further experiments). The 

 offspring were all agouti-colored like the wild father; 39 such | wild 

 offspring were obtained, but of these only 10 females were successfully 

 used for breeding purposes. The males were all sterile. 



I have used the terms ^ wild, J wild, | wild, ^t wild, etc., but wish 

 to state here that these terms are used only for convenience, without 

 implying blending inheritance. They simply denote the generation 

 to which a hybrid belongs. 



ONE-QUARTER WILD HYBRIDS. 



Since the | wild males were sterile, the | wild females were mated 

 to both parent stocks. When mated to the guinear-pig they produced 

 i mid rufescens hybrids; but when mated to the wild Cavia rufescens 

 they produced | wild rufescens hybrids. Of the J wild young 83 were 

 obtained, sired by pedigreed male guinea-pigs. In this blood the males 

 were again sterile; therefore the females were mated back to guinea- 

 pig males. The numbers of sexually mature females increased with 

 each generation; hence there was no difficulty in procuring sufficiently 

 large numbers of the more dilute-blooded hybrid animals. 



THREE-QUARTERS WILD HYBRIDS. 



Only one wild male (cf 24) and one f wild female (9 50) were used for 

 this part of the experiment, and they produced four young, of which 

 two, a male and a female, reached maturity but proved to be sterile. 

 (See fig. 3.) The wild males died out soon after this, and effectually 

 put an end to this class of matings. 



ONE-EIGHTH WILD HYBRIDS, AND LATER GENERATIONS. 



Proceeding in the same manner used to obtain the previous genera- 

 tions, the females of one blood were continually mated back to guinea- 

 pig males to produce animals of the next blood-dilution. Thus, from 

 ovx I wild females we obtained ^ wild, and from the | wild females we 

 obtained ^V ^Id. Up to the time of writing, the blood has been 

 reduced to ytt "^Id, with -j-fr "^d young in utero; i. e., the Fg genera- 

 tion. Naturally most of the animals now living are not so far removed 



