282 ZOOLOGY SECT. 



duced in immense numbers, and are impregnated within the body 

 of the female. The sperms are non-motile, or perform amoeboid 

 movements only after entering the female organs. Cilia are 

 wholly absent. 



A large proportion of Nematoda are free-living, spending their 

 whole life in fresh- or salt-water, damp earth, decaying matter, 

 &c. ; the remainder are parasitic during the whole or a part of 

 life. 



The class is divided into two orders. 



ORDER 1. NEMATOIDEA. 



Nematoda in which the coelome is not lined by epithelium, but 

 is bounded directly by the body-muscles. There are two chief 

 nerve-cords given off backwards from the pharyngeal ring and 

 lying in the dorsal and ventral lines. There are two excretory 

 canals lying in the lateral lines and opening anteriorly and 

 ventrally. The gonads are continuous with their ducts and con- 

 sist of long, more or less convoluted cords. This order includes 

 the whole of the free-living Nematodes as well, as the large 

 majority of parasitic forms. 



ORDER 2. GORDIOIDEA. 



Nematoda in which the coelome is lined by a distinct epithelium. 

 The pharyngeal nerve-ring sends off a single large ventral nerve- 

 cord well supplied with nerve-cells. The gonads, or at least the 

 ovaries^ are arranged metamerically, and the reproductive products 

 ate discharged into the body-cavity and pass thence into the 

 gonoducts. This order includes a small number of greatly 

 elongated thread-like worms which are parasitic in the asexual, 

 free-living in the sexual stage. 



Systematic Position of the Example. 



Ascaris lumbricoides is one of many species of the genus Ascaris, 

 and belongs to the family Ascaridce of the order X<'nifit<>iili'n. 



The absence of an epithelial lining to the body-cavity, and the 

 presence of elongated gonads continuous with their ducts, indicate 

 its position as one of the Neinatoidea. Among the numerous 

 families constituting this order the Ascarida? are distinguished by 

 the possession of three lips furnished with papilla?, and by the 

 body of the male being curved ventrally. Ascaris is distinguished 

 from the other genera of the family by the absence of a bulb-like 

 enlargement at the posterior end of the pharynx, by the posterior 

 extremity of the body having the form of a short blunt cone, and 

 by the presence of two penial seta? in the male. 



