MOODIE: TURTLES AND PLESIOSAURS. 321 



the neck. The body portions remain as they are, and three are 

 lost from the tail. The manner of development of the tail 

 is not of importance in this connection, so that will not be 

 discussed here. So far as I can learn, Parker's observations 

 as to the large number of somites in the neck have never been 

 confirmed. They certainly are not confirmed by the figures 

 given by Rathke and Agassiz. Nor am I able to find any indica- 

 tion of supernumerary segments in the twoscore or more em- 

 bryos I have examined, both in sections and whole. I am at a 

 loss to explain Parker's observations, unless it be that his 

 material was pathological. He had only a few specimens at 

 most, and he fails to state how many show this remarkable 

 character. I have carefully examined embryos of several gen- 

 era of turtles and find nothing unusual in any of them. Be- 

 fore the cartilage is laid down for the vertebrse there are, of 

 course, the somites, but I have never detected any unusual 

 number nor have I seen more than eight cartilages for the 

 vertebrse of the neck. So far, then, as the evidence goes, 

 Parker's results are at variance with the results obtained by 

 others. It can at least be said that the condition described by 

 him for the embryo of CJidone viricHs Schneid. does not apply 

 to the other turtle embryos examined, and it is to be greatly 

 doubted if there are ever more than the usual number of seg- 

 ments in the normal embryo. So far as I can learn there are 

 no evidences of a reduction, ontogenetically, of the number of 

 segments in the neck of any form, although such has been 

 claimed for some of the birds. It is a matter which is easily 

 conceivable that the loss or addition of vertebrse in the column 

 may take place, and Baur has cited a few such cases. This is, 

 however, by intercalation, and just what its significance is I 

 do not know. Such an instance has never, I believe, been 

 recorded for the turtles, and there is no evidence that the 

 Chelonia ever had more than eight cervicals, while the plesio- 

 saurs had from thirteen to seventy-six. 



Teeth have never been discovered in the turtles. Marsh, it 

 is true, described^ the anterior portion of a peculiar mandible 

 which he suggested might belong to the Chelonia. He says: 

 "So far as now known, they appear to be nearest allied to the 

 Chelonia, although turtles without teeth occur in the same 

 strata with them." Hay says the fossil is problematical, and 

 locates the form, MacelognatJms vagans Marsh, among the 



4. Marsh, 1884, Amer. Jour. Sci.. ii. 341. 



