CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 121 



cup-sliaped, but still without color, border, and lobes. The muscular 

 oesophagus is very long and cylindrical. The intestine, which extends 

 in a straight line from the termination of the uisophagus to the anus, 

 fills almost the entire body, and is already colored red ; near the an- 

 terior third of the body may be seen a fleshy thickening, which sends 

 a prolongation forward beyond the posterior extremity of the oesopha- 

 gus, and one, longer than the first, backward toward the caudal ex- 

 tremity. This is the rudiment of the sexual organ. 



This discovery of the nymph enables us to say that all the develop- 

 mental phases of Syngamns tracheaUs are now known. The only two 

 media which this i)arasite inhabits during its entire existence are the 

 water or moist earth during its embryonal condition, and the respira- 

 tory organs of its victim during its nymphal and its adult phase. It is, 

 therefore, developed without the aid of any other medium than the 

 water, corresponding in this respect to the immense majority of vermin- 

 ous parasites. 



