214 



NEMATHELMINTHES 



Key to the classes of Nemathelminthes : 



Ci No spinj' proboscis at forward end ; intestine present. 



61 Mouth and intestine not degenerate in adult ; lateral lines present. 



1. Nematoda 



62 Mouth and intestine degenerate; lateral lines absent 2. Gordiacea 



Oj Spiny proboscis present ; no intestine 3. Acantiiocephala 



Class 1. NEMATODA.* 



Threadworms (Fig. 344). Round, slender worms, usually white 

 or flesh color in appearance, which vaiy from microscopic size to a 

 meter in leng-th. The integument consists of a cuticula 

 which is usually smooth on the outer surface and a soft 

 subcuticula; no hypoderniis is present, but the subcuticula 

 is supposed to represent it. There is a voluminous body 

 cavity into which the subcuticula projects along the 

 median dorsal and ventral and the two lateral lines, 

 forming thus 4 prominent longitudinal ridges. In the 

 lateral ridges run the paired excretory canals, which open 

 to the outside by a pore just behind the mouth, and the 

 lateral nerve cords; and in the dorsal and ventral ridges 

 are also nerve cords. Lying next the subcuticula is a 

 single layer of characteristic, longitudinal muscle fibers, 

 no circular fibers being present. The nervous S3^stem con- 

 sists of a nerve ring containing ganglion cells which sur- 

 rounds the oesophagus and a number of longitudinal nerves 

 extending both forwards and backwards, those going back- 

 wards being joined by transverse commissures. The only 

 special sense organs are simple eyes, which some nema- 

 todes possess, and also sensory papillae. 



Tlie body cavity is without mesenteries, transverse 

 septa, or peritoneal lining and contains blood. Lying in 

 it are the alimentary canal and the reproductive organs. 

 The mouth is at the forward end of the body and may be 

 sun'ounded by sensory lips or papillae, and armed with 

 chitinous teeth. The oesophagus is a muscular sucking- 

 organ into which a pair of long glands may open; its 

 hinder end may be constricted, causing the formation of one or two 

 swollen divisions, called oesophageal bulbs. The intestine is a straight 

 tube which passes to the anus near the hinder end of the body. The 



* See "Monographie der Nematoden," by A. Schneider, 1866. "Die Siisswasser- 

 fauna Deutschlands," by L. A. Jagerskiold and O. von Linstow, Heft 15, 1909. "The 

 Nematodes Parasitic in the Alimentary Tract of Cattle, Sheep," etc., by B. H. Ran- 

 som, Bull. 127, Bur. An. Ind., 1911. 



Fig. 344 



Diagram of 



female 



nematode 

 (Siissw. F. 



Deut). 



1, mouth 



2, nerve ring 



3, oesophagus 



4, excretory 



pore 



5, intestine 

 6, ovary 



7, genital pore 

 8, anus. 



