292 



THE AMEBIC AN NATURALIST 



[Vol. LII 



culty has been found in maintaining approximately the 

 original numbers of the other two races, despite the steril- 

 ity of a large proportion of the individuals. Here, then, 

 we may note in passing, is another interesting racial dif- 

 ference of a physiological nature. 



This deterioration of the stock, it must be pointed out, 

 is progressive. Each generation probably presents more 

 abnormalities than the preceding one. The causes of this 

 condition are at present entirely unknown to me. Mal- 

 nutrition or intoxication, resulting from pathogenic bac- 

 teria or protozoa in the alimentary canal, may be men- 

 tioned as possibilities. Many of the animals are now 

 being reared in small open pens, where they are allowed 

 to burrow in the ground. A preliminary test of this plan 

 encourages us to hope that the troubles referred to may 

 thus be avoided. 



The following table presents mean values for certain 

 characters in the C 2 generation, for the three races which 

 are now being reared at La Jolla. 



TABLE V 



It is plain from this table that, in respect to the four 

 characters other than body length (tail length, foot 

 length, ear length and tail-stripe), the three races have 

 maintained the same relative positions in the series as 

 formerly. When arranged with reference to tail, foot 

 and tail-stripe, the series, as before, is : Eureka > La Jolla 

 > Victorville. As regards ear length, the earlier arrange- 

 ment likewise holds, viz. : 



T T 11 f Eureka, 

 La Jolla > i Tr . . ' 



I V ictorville. 



Another significant fact does not appear from the fore- 

 going table, however. The modifications of the three 



