3 end of the 



The shield begins to develop by a budding out laterally of the 

 musculo-cutancous layer along the sides of the body, and the 

 growth of narrow ribs extending to the edge of the shield. "The 

 feet, or rather paddles, of the lower forms of turtles, the Chelon- 

 ioidae, do not remain in a partially undeveloped state, as might be 

 expected from what is observed among other vertebrates, but un- 

 dergo what may be called an excess of development ; the bones 

 of the toes becoming very much elongated, and the web— which 

 rerr s ft n ; turtles with moderately elongated toes, 



that the whole foot is almost as rigid as the blade of an oar. At 

 this time the embryo of Chdydra serpentina snaps at everything 

 which touches it. 



Of the development of the Sauriasis, or lizards, we have no com- 

 plete account. The advanced embryo of the lizard, as figured by 

 Owen (443), is like that of the turtle without its shell. 



As regards the development of snakes, Owen, deriving his in- 

 formation from Rathke's work, tells us that in the oviparous 



e_-_ ; - !:■; v..\r.-- ■ > - : : -- ■ :■■ : ■■ ■ ' ■ > ■■■ ■ : - 

 deposited. By this time the amnion is perfected, "the head is 



in 1 ma mlar processes 11 t 1 s is ab shir-, s the 



head." The long trunk of the serpent grows in a series oi de- 



• ; ■ , : . ' . . ; - ■; - ; . a: v.,- 



latter third of embryonic life the right lung appears as a mere 

 appendage to the beginning of the left. 



A summary of the changes in the egg undergone by the reptiles 

 is as follows: 



1. Segmentation partial, possibly total (morula?). 



embryonal membranes appear. 



3. Formation of an amnion. 



4. After the alimentary canal is sketched out, the allantois buds 



