REPTILIA. 



323 



interior, except after some of the fluid con- fetus, here represented with its limbs folded up in 

 tents have been permitted to evaporate. The their natural . position ; b, the allantois, with its 



enclosed ramifications of blood- vesse's; c, the yolk, 



Fig. 242. which is in communication with the intestinal canal 



by means of the vitelline duct, which enters the 

 abdomen through the opening of the navel. 



state of maturity, the disposition of the 

 allantois and of the vitelline sac is found 

 to be precisely similar to that of these 

 structures in the egg of a bird, as will be at 

 once evident on reference to the annexed 

 figure, representing the anatomy of the ovum 

 of the Monitor at a very advanced state of 

 maturation. 



The allantoic sac, which serves for the 

 respiration of the embryo during the earlier 

 stages of its growth, is richly vascular, and 

 communicates as usual with the anterior part 

 of the cloacal cavity, the so-called urinary 

 bladder being, in fact, merely a remnant of 

 this apparatus. 



The vitelline sac communicates freely with 

 the abdominal cavity at the umbilicus, . its 

 contents being conveyed into the commence- 

 ment of the intestinal canal through a ductus 

 vitello-intestinalis (fig. 244, <?) : at a still later 



Fig. 244. 



Egg of the Monitor laid open at a late period of 

 Incubation. 



a, the yolk; b, the amnion; c, umbilical cord; 

 d, the embryo, remarkable for the beautiful " pack- 

 ing " of its limbs and tail ; e, the pergamentaceous 

 egg-shell. {After Cams.') 



vitellus exhibits a cicatriciila, surrounded with 

 a double zone. 



When the embryo arrives at a sufficient 



Fig. 243. 



Embryo of Emys amazonica. The shell has been 

 removed and the membranes of the egg laid open 

 and spread out. 



a, the amnion, turned back so as to display the 



Anatomy of a very young Fetus of the Viper 

 ( Vipera Berus). (After Otto.) 



a, the yolk-bag , b, the amnion ; c, the umbilical 

 cord; d, ductus vitello-intestinalis; e, opening of 

 the ductus vitello-intestinalis between the longi- 

 tudinal folds of the mucous membrane of the small 

 intestines ; /, intestine partially laid open and cut 

 across ; g, h, continuation of the intestine as far as 

 the anus ; i, i, rudiments of the ovaria ; k, k, the 

 kidneys ; I, anus. 



Y 2 



