VARIATIONS IN AGOUTI PATTERN. 



99 



two hypotheses. Cross 10 gives the results of the tests of light-bellied 

 young from such a cross as described (table 44). 



Table 44. 



In no case has the same animal had both ticked-bellied and non- 

 agouti young. Some of those which have had ticked-bellied young 

 have been quite thoroughly tested. Male M138 had 20 light-bellied 

 and 19 ticked-bellied young. Male B121 had 13 light-bellied and 13 

 ticked-bellied young. Male M91 had 5 light-bellied and 11 ticked- 

 bellied young. The chance that these can represent 2:1:1 ratios is 

 negligible. Thus hypothesis (I) may be dismissed. 



Light-bellied agoutis demonstrated to carry ticked-belly have been 

 crossed inter se (cross 11). They have given 25 light-bellies and 9 

 ticked-bellies, no non-agoutis. This agrees reasonably well with the 

 expected 3 to 1 ratio. The remaining tables give the results of miscel- 

 laneous crosses. All of them are in harmony with the hypothesis of 

 triple allelomorphs. 



MINOR VARIATIONS. 



Thus there seems no doubt that the light-bellied agouti of Cavia 

 porcellus, the ticked-bellied agouti of C. rufescens hybrids, and non- 

 agouti form a series of triple allelomorphs. The question remains 

 whether light-bellied Cavia rufescens hybrids possess a different allelo- 

 morph from the ticked-bellied ones, or whether the difference lies 

 simply in the residual heredity. There are no wholly satisfactory data 

 bearing on this point. Nevertheless the fact that the darkening seems 

 associated especially with certain stocks of guinea-pigs seems to favor 

 the second view. The writer has crossed ticked-bellied agoutis re- 

 peatedly with the intense blacks of BB or BW stock. Young have 

 been obtained which were self black, except for a few ticked hairs in the 

 chest and whiskers. One ignorant of their history would probably 

 have classified several of them as blacks. Before they became adult, 

 however, these black ticked-bellies acquired a uniform though very 

 slight yellow ticking throughout the entire fur. On crossing such black 

 ticked-bellies with a dull black stock (4-toe) there is a return to a more 

 strongly developed agouti pattern. The young are uniformly ticked 

 when born. Thus these variations in the agouti pattern seem related 

 to the residual heredity of the stocks, possibly with the same residual 

 heredity which determines the very intense development of pigment, 



