The Rodent ia in Evolution. . 63 



short orwantingjthe sacrum stoutly anchylosed to the pelvic 

 bones. Many of these characters are obviously favorable 

 to a fossorial animal. They are possessed in toto by some 

 rodents, as for instance, the male Bathyergus, and in 

 part by others, as, for instance, the pocket gopher, but 

 they are hardly possessed by the striped gophers, Sper- 

 mophilus 13—lineatus, hardly differs in any respect from 

 the ground and tree squirrel, though Franklyns gopher, 

 Spermophilus franklyni, does present enlarged nail on the 

 fingers and somewhat stouter limb bones than the striped 

 gopher. And these facts would seem to mean that evolution 

 has taken place, and in some gone further in production of 

 variety of structure than in others, that some are more com- 

 pletely specialized, while others are now in the act of special- 

 izing, and others hardly begun. 



Almost all the rodents in the species, genera and families, 

 can be arranged in series, which lead from less specialized 

 centre on more and more specialized radii to highly special- 

 ized final terms. The ground squirrel, the tree squirrel, the 

 flying squirrel, and the anomalure, form such a series, start- 

 ing from a point the ground squirrel, from which also we 

 can proceed toward the spermophile, the marmot, the prairie 

 dog, and finally the sewelled. The ground squirrel or some 

 similar form is also a possible starting point toward similar 

 centres in the hystricomorpha and myomorpha,but here the 

 immediate terms are not yet known; perhaps they are 

 wholly lost and will never be known ; but it is not wholly 

 certain that they may not some day be found, or their 

 remains be found, if they existed and are now extinct. 



It is not possible in the limits of this paper to refer to 

 many other cases similar to the fossorial. The case of the 

 development of the leaping habit has already been presented 

 before this Academy. A very large amount of study of the 

 rodents from this standpoint is necessary before the question 

 can be thoroughly examined. Only one more point in con- 

 clusion. My attention was directed to this whole subject 

 several years ago during the agitation which was then so 

 very lively between the New Lamarkian and the Post Dar- 

 winian schools of evolution. Professor Cope, the leading 

 exponent of the former, seeking a cause of the appearance of 



