IO8 H. H. NEWMAN. 



ment, one dark spot at the median posterior margin of each scute, 

 i. c., at the keel (see Fig. 56). Later on two or more other spots 

 of a similar appearance are produced in very definite positions on 

 the various scutes. These secondary spots never become quite 

 so prominent as the primary ones, but continue to develop like 

 the latter into concentric ocellated markings (Fig. 57). The rings 

 that constitute these ocellated spots are formed by repeated split- 

 ting of the innermost ring of pigment, in brief are proliferated 

 from a center of pigment deposit. After three or four cencentric 

 rings have been laid down, a well-marked unpigmented band ap- 

 pears on the periphery of the whole spot. It is this light band 

 that produces the most pronounced secondary complexity, for it 

 sends out processes to neighboring spots and forms the charac- 

 teristic reticulated pattern that has given the name " map-turtle " 

 to the species. In the marginals the pattern is not so complex, 

 since no secondary spots appear. The concentric rings of the 

 primary spot, however, often take on fantastic shapes that all but 

 obscure the original unity of the coloration. It is very interest- 

 ing to note that the spots in the marginal series are found as a 

 rule half on one scute and half on the next, so that the light per- 

 ipheral band that separates adjacent spots frequently coincides 

 with the sutures of the dermal plates beneath. The spots then 

 occupy the growth centers of the plates and no longer hold any 

 close relationship with the scutes. Pigmentation scans to be inti- 

 mately connected with dermal ossification. The scutes must have 

 grown away from their original positions, thus overlapping the 

 sutures of the plates, and lending strength to the general struc- 

 ture. The direction of movement has been forward, as is found 

 by examination of the first pair of marginal scutes that run over 

 upon the nuchal plate. The original cause of the forward move- 

 ment was, I believe, the increase in size of the nuchal plate which 

 must have pushed back the marginal plates. The scutes would 

 of course occupy their original positions or would continue to 

 crowd the nuchal scute into a still smaller space. 



That the primary ocellated spots denote centers of dermal ossi- 

 fication will, I believe, be admitted. What then is the signifi- 

 cance of secondary ocellated spots, which have an exactly simi- 

 lar appearance and method of development ? They must, I 



