HEPTlLEg 



S60 



be withdrawn. The Chelonia are divided into two sub-groups — of the 

 first, wherein the vertebrae and ribs are free from the carapace, 

 Dermochelys coriacea, a huge marine turtle sometimes 6 feet in length, 

 widely but sparsely distributed in tropical seas, is the sole representa- 

 tive. The second group, with dorsal vertebrae and ribs fused in the 

 carapace, comprises the chelonidj]], marine and amphibious turtles 

 with paddle-like flippers living on or near the shores of tropical seas, 

 and the testudixid.e, land tortoises with feet provided with toes 

 adaj^ted for walking, found widel}^ in the warmer regions of the 

 Eastern and Western Hemispheres (Fig. 444) ; among these the 

 terrajDins form an intermediate group with webbed toes. 



Turtle 



0t a^w*-' '-■"■ " i». 



Fig. 444. — The Head of the Tortoise, Testudo (Katharine Taiislej'). 



The eyes of the Chelonians, described and beautifully figured by 

 Albers (1808) and Soemmerring (1818), and intensively studied by 

 Kopsch (1892), bear a close resemblance to the lacertilian eye just 

 described, but in general are more simi^le in structure ; there are, 

 however, some major difl^erences — the i^resence, of ciliary processes, the 

 participation of the sphincter pupillce in the act of accommodation, and 

 the absence of a conus (Figs. 445 and 446). 



The GLOBE is comj)aratively small and the cornea, instead of 

 projecting forwards, continues the curvature of the sclera so that the 

 corneo -scleral sulcus is insignificant. The epithelium is thick. Bowman's 

 membrane absent and the endothelium markedly developed (Fig. 448). 

 The scleral ossicles are imbricated in several layers so that the edge 

 of one lamella is inserted ]:)etween two others. Their numbers vary 

 from 6 to 15,^ while the scleral cartilage is very thick (1 cm. in the 



1 The scleral ossicles number 6-9 in the Greek tortoise, Testudo grceca ; 10 in the 

 tortoise, Emys (Konig, 1934) ; 15 in the Mauritius tortoise (Rochon-Duvigneaud, 

 1943) ; and so on. 



S.O.— vol. I. 



24 



