Diversity in the Scutes of Chelouia. 69 



_ Inheritance from Immediate Ancestors. 



The diversity in some of the lots of turtles, each of which groups 

 came from one original nest (Tables VI and VII, A, B, and C) cer- 

 tainly does not suggest that the abnormalities of the parents had a 

 great influence on the abnormalities of the young, but on this point, 

 again, the data are inadequate. 



Atavism. 



It has been seen that the prevailing interpretation of the abnormal 

 scutes is that they are atavisms ; ^'reminiscences of earlier, phylo- 

 genetic conditions" (Gadow, '05, p. 638) ; ''examples of systematic 

 atavism in the sense of de Vries" (Ne^vTiiann, '06, p. 69). In study- 

 ing this diversity of scutes, then, one is confronted at the outset by 

 these questions : are all of the abnormalities to be regarded as 

 atavisms ? and, if not all, which anomalies are due to reversion ? 

 Comprehensive use of the conception of "systematic atavism," as 

 applied to these variations, has been made for morphological pur- 

 poses, and as the observations given in this paper might be taken 

 some to confirm, some to modify, others to negative such morpho- 

 logical views, I consider it necessary to inquire with some fulness 

 regarding the basis of the atavistic interpretation of supernumerary 

 scutes. 



It has already been made clear that asymmetrical neurals are not 

 to be regarded as instances of reversion. Further, from a glance at 

 such figures as Figs. 63, Q>Q>, and 95, w^e infer that some others 

 of the abnormalities are surely not referable directly to atavism. 

 But, are most of the supernumerary scutes to be explained by rever- 

 sion ? and, hy tvliat criterion shall it he decided if a given scute is 

 atavistic or coenogenetic in character? 



By atavism we understand ordinarily the reappearance of a char- 

 acter, not manifest in the immediate ancestors, but typical of some 

 remote ancestral form. It is assumed that this character, though 

 disappearing from view, has never been actually lost, but, having 

 assumed a latent condition, has been transmitted from generation to 

 generation until finally, on the proper occasion, it reasserts itself. 

 Atavism is, therefore, much more than a descriptive term referring 



