72 Kobert E. Coker. 



appear in three embryos of the loggerhead turtle, taken from arti- 

 ficial nests, and the resemblance to the same abnormality in man and 

 in Triton is striking. Here is the same abnormality occurring in 

 different and widely removed species, and with remarkable defini- 

 tions of form. 



The matter of recurrence need present little difficulty. If the 

 organization of one turtle is much the same as that of another of 

 the present time or of a considerable period of past time (and observa- 

 tions so indicate), I do not know why turtles may not be subject to 

 similar anomalies ; nor why there may not occur now the same varia- 

 tions that once, in connection with others, characterized the ancestors 

 of a diverging species ; nor why, if any of the variations now occur- 

 ring should characterize a future subspecies or species, they might not 

 continue to occur in other turtles without acquiring a new sig- 

 nificance. 



3. The use of the supposed atavisms as morphological data 

 implies not only the transmission of the primitive characters in latent 

 condition from generation to generation since remote geological ages, 

 but also that they are now seen practically in pure form and unmixed 

 with any appreciable number of new inheritable variations, occurring 

 first during these ages since the primitive characters became latent. 

 The ground for such an assumption is not apparent. 



4. From the phylogenetic point of view, how far back nuist the 

 atavism of scutes point ? The whole matter of the phylogeny of tur- 

 tles is obscure, but, from paleontological data, it is evident that the 

 carapace of Thecophorous turtles acquired at quite a remote period 

 very nearly the present form as regards arrangement of scutes and 

 plates. Existing genera may be traced back to Eocene {Tlialas- 

 sochelys) and Upper Cretaceous periods (Chelone). More sig- 

 nificant still are such fossil forms as Plesiochelys solodurensis Ruti- 

 meyer, and Platychelys oherndorferi Wagner, from the Upper Jura, 

 with carapaces showing essentially the saine plan of scutes and plates 

 as is found in turtles of to-day, except that the dovetailing of neural 

 and costal scutes is less noticeable. I should be slow to draw infer- 

 ences from the variations in modern turtles regarding the types of 

 periods more remote than the Upper Jura. 



