G38 



ANATOMY OF VERTEBRATES. 



449 



in the embryo Serpent: e is the leathery and partially calcined 

 egg-shell. An embryo Lizard, at an earlier period of develope- 

 ment, is shown in fig. 443. 



Hunter left the following preparations illustrative of the 



developement of the Cro- 

 codile. No. 3364 shows the 

 calcareous outer crust of 

 the inner 'membrana puta- 

 minis' of the ego; : No. 3365 

 shows the attachment of the 

 vascular allantoisto that shell 

 membrane in an embryo in 

 which part of the yolk has been 

 received within the abdomen. 

 In No. 3366 the hinder half 

 of the Crocodile is dissected 

 to show the condition of the 

 vitelline and allantoic sacs at 

 the close of foetal develope- 

 ment : the vitellicle presents 

 an irregular lobated form, 

 and its short and narrow 

 duct communicates with the 

 small intestine a little below 

 the duodenum : the allantois 

 communicates with the lower 

 and fore part of the cloaca 

 by means of a long and slender duct homologous with the urachus : 

 but no part is dilated, as in certain Lizards, to form the urinary 



bladder. In No. 3370 is shown the 

 vitellicle, after inclusion within the 

 abdominal Avails ; it is much red viced 

 in size, and its contents are hard and 

 stringy. 



The period of external incubation 

 by the action of the sun's rays upon 

 the sand-nest of the eggs of the 

 Turtle (Chelo?ie Midas) has been 

 ascertained to be seven weeks. 



Figure 450 shows the embryo 

 of a Snapping Turtle {Chelydra 

 serpentina) from an egg laid June 21st and opened September 21st 

 of the same year. The amnios is cut away : c shows the ' area vascu- 



Egg and embryo of the Monitor Lizard, xliii. 



450 



Embryo Tortoise, Chrtyflra m rpi uti in. ccc. 



