NEMATOIDEA. 43 



in a state of inertia. The embryo remains enclosed 

 within the shell, from which it never issues spon- 

 taneously ; it lives there for more than a year, so 

 that in those cases in which the ovum is slowly 

 developed, more than two years may elapse between 

 the formation of the ovum and the termination of 

 embryonic existence. 



According to Dr. Davaine's experiments, made 

 upon dogs, it appears that the eml^ryo remains shut 

 up in the shell until the ovum is brought again into 

 the intestines, and that, when it has arrived at this 

 situation, the action of the intestinal juices soften 

 the shell, which is pierced by the embryo, so that 

 the latter is finally liberated. 



The Ascaris lumbricoides lives in the small intes- 

 tines. 



Ascaris Alata (Bellingham). 



The female of this species is about three a,nd a 

 half inches in length ; its anterior extremity is bent, 

 and furnished with two semi-transparent winglike 

 expansions (whence the name), about one-tenth of 

 an inch long ; the tail is conical, and marked by a 

 black spot. 



Two females of tliis species have been observed 

 on one occasion only by Bellingham, of Dublin, who 

 states that he believes that the same species had 

 been previously observed by Dr. J, Y. Thompson. 

 According to Dujardin, these entozoa are very similar 

 to the ascaris of the cat, Ascaris mystax.^ 



^ In an interesting paper contained in the " Lancet " of 

 Jan. 10, 1863, Dr. Cobbold supports this view, and shows that the 

 A. alata is more common in the human subject than it is generaUy 

 supposed to be. 



