"ABNORMALITIES" IN CHELONIA. 



VI. THE COLOR PATTERN OF CHELONIA AS CONFIRMATORY EVI- 

 DENCE FOR THE FORMER EXISTENCE OF A DERMAL ARMOR. 



Evidence is not lacking that points to an original striped con- 

 dition of the chelonian carapace. The neck and tail of most 

 tortoises show characteristic stripes which on careful examination 

 may be analyzed into rows of scales with similar coloration. 

 When the scales are large enough, it will be seen that each has a 

 center of pigmentation coinciding with its center of growth. Now 

 the coloration of the carapace and plastron is nothing more than 

 a series of scales or scutes, each with its pigmental center. The 

 striped effect is lost through the great increase in the size of 

 the scute and the consequent separation of the centers of pig- 

 mentation. 



The pigmentation of scutes is typically concentric in character, 

 whether the pattern consist, as in CJielydra and Aroinoc/ielys, of 

 radiating bands of pigment having their center located at the 

 center of scute growth, or concentric rings as in Graptcmys, or 

 lastly, of a light area occupying the center of growth, and all 

 the rest solidly colored, as in Clcmnys guttatits. 



Frequently a great complexity of marking arises through the 

 secondary complications of primary markings, but these conditions 

 are seen in a simplified condition in the developmental stages. 



It strikes one very forcibly that there is an intimate relation 

 between scute growth and pigment distribution. The two 

 processes have a common center and go hand in hand. The 

 areola, or egg-plate (see Fig. 57, dotted lines) forms a convenient 

 locus for measuring both processes. This location corresponds, 

 curiously enough, with the keel of the scute and hence with the 

 center of dermal ossification. 



An examination of embryos of CJielydra shows that the colora- 

 tion consists of dark patches of melanin pigment at the tip of the 

 tubercular processes of the keels. The marginals are marked 

 with small black spots at the posterior edge of each scute, some- 

 times running back over the anterior margin of the next scute. 

 Specimens of CJielydra ?L year or two old have a radiating pattern 

 with the center of pigment proliferation' at the keel. In older 

 specimens a solid coloration obscures everything. 



Older embryos of Graptemys have, as the first indication of pig- 



