V 



174 CHELONIA. 



the coils are supplied by the tail. There are in all at this stage 

 seven coils, and the spiral is right-handed. 



Another point, which deserves notice in the Snake, is the absence 

 in the embryo of all external trace of the limbs. It might have been 

 anticipated, on the analogy of the branchial arches, that rudiments of 

 the limbs would be preserved in the embryo even when limbs were 

 absent in the adult. Such, however, is not the case. It is however 

 very possible that rudiments of the branchial arches and clefts have 

 been preserved because these structures were functional in the larva 

 (Amphibia) after they ceased to have any importance in the adult ; 

 and that the limbs have disappeared even in the embryo because in 

 the course of their gradual atrophy there was no advantage to the 

 organism in their being specially preserved at any period of life 1 . 



3 Chelonia 2 . In their early development the Chelonia resemble, so 

 far as is known, the Lacertilia. The amnion arises early, and soon 

 forms a great cephalic hood. Before development has proceeded 

 very far the embryo turns over on to its left side. The tail in many 

 species attains a very considerable development (fig. 133). The chief 

 peculiarity in the form of the embryo (figs. 131, 132, and 133) is 

 caused by the development of the carapace. The first rudiment of 

 the carapace appears in the form of two longitudinal folds, extending 

 above the line of insertion of the fore- and hind-limbs, which have 

 already made their appearance (fig. 131). These folds are sub- 



Ir.l 

 Jlit, 



u 



FIG. 131. CHELONE MIDAS, FIEST STAGE. 



Au. auditory capsule; br. 1 and 2, branchial arches; C. carapace; E. eye;/./', 

 fore-braiu; f.l. fore-limb; H. heart; h.b. hind-brain; h.l. hind-limb ; hy. hyoid; m.b. 

 mid-brain; mn., mandible; mx.p. maxillo-palatine ; N. nostril; u. umbilicus. 



sequently prolonged so as to mark out the area of the carapace on 

 the dorsal surface. On the surface of this area there are formed the 



1 It is very probable that in those Ophidia in which traces of limbs are still 

 preserved, that more conspicuous traces would be found in the embryos than in the 

 adults. 



- Vide Agassiz (No. 164), Kupffer and Benecke (No. 154), and Parker (No. 165). 



