92 ON THE PHYSIOGNOMY OF SEIirENTS. 



by several physiologists, has been regarded by otiiers 

 as analogous the Chorion.* Probably this tunic is com- 

 posed, as in the eggs of Tortoises, of two lamellae, the ex- 

 terior of which, containing the bloodvessels, may perhaps be 

 compared to the chorion of the embryon in mammifera, 

 while the interior is the true allantois."f The embryon it- 

 self is shut up in a serous membrane, the amnion. The 

 canal of the vitellus enters the small intestine near the py- 

 lorus ; biit the umbilical opening is not always found oppo- 

 site to that region: in the Trigonocephalus atrox, where it is 

 near the anus, the canal of the vitellus is obliged, in order 

 to enter the duodenum, to mount in the interior of the ab- 

 dominal ca^^ty the whole length of the intestines. 



The nmnber of young which Ophidians produce at a 

 single deposition of eggs, differs considerably in the different 

 species. I have observed in several Calamaria; not more 

 than ten ; some Colubri lay from twenty to twenty-five ; 

 I have found thirty and more in the Trigonocephalus atrox, 

 and it is said that our Ringed Snake lays as many as 

 forty. On opening the belly of a pregnant snake we see 

 the eggs, impacted one against the other, and arranged in 

 masses, occupying in all their length the oviducts, which 

 then resemble a necklace. The embryon has all its tegu- 

 ments colourless, and the eyes extremely developed and 

 salient ; the head is rounded, the muzzle short, sloping, 

 and resembling that of a dolphin or of a fowd. In pro- 

 portion as the foetus is developed, so much nearer does its 

 form approach to that of the perfect animal. To disengage 

 itself from its prison, the young snake, probably by the 

 power of its movements, ruptures the tunics which inclosed 

 it. This operation it can easily perform when the coats are 

 membranous, as in the viviparous species ; but it must require 

 great efforts to burst the coriaceous envelope of the true 

 egg : three or four longitudinal rents, near the end of the 



* It is for this reason that some deny the existence of the allantoid 

 in the eggs of the Ophidians, while others maintain the contrary : com- 

 pare DESMOULiN's,Ll/em. de la Soc. Med. ; Rathke, ap. ; Burdach, Phys, 

 \i., p. 409 and 563 ; Herholdt, Oversigt, &c. 



t TiEDEMANif^ Juhelfeier, p. 25. 



