360 THE ANIMAL PARASITES OF MAX 



C. NEMATHELMINTHES. 



JJY 



J. W. W. STEPHENS, M.D., B.C., D.P.H. 



BILATERALLY symmetrical animals, without limbs and with a body cavity in 

 which the gut or other organs float. They are generally cylindrical. 



Class. NEMATODA. 

 Nemalhelminthes with an alimentary canal. 



Nematodes are as a rule elongated round worms of a filiform or fusiform shape ; 

 their length varies according to the species from about i mm. to 40 to 80 cm. 

 The outer surface of the body is smooth or annulated, and at certain points provided 

 with papillae, occasionally also with bristles and alar appendages. The anterior end 

 carrying the oral aperture is usually rather slender, occasionally quite thin ; the 

 posterior end is pointed or rounded ; the anus, as a rule, lies somewhat in front of 

 the posterior extremity. The sexes are almost always separate, and the male can 

 as a rule be easily distinguished from the female because the former is smaller and 

 more slender, its posterior extremity is often spiral or incurved, or carries an alar 

 appendage, whereas the female is larger and thicker, and its posterior extremity 

 is straight. In the male the genitalia open into the anus ; the sexual orifice of the 

 female opens ventrally along the median line in the anterior half of the body, in the 

 middle, or a little further back. Both sexes, moreover, have an orifice, the excretory 

 pore, which is situated ventrally in the median line and about the level of the 

 cesophageal nerve ring. 



In large species, even with the naked eye, two lighter transparent bands the 

 lateral lines may be distinguished ; they run along the sides of the body from the 

 anterior to the posterior end, while two other bands, the median lines, running 

 along the ventral and dorsal mid-lines,, are less evident ; in exceptional cases there 

 are also four sub-median lines. These bands or lines are inward projections of the 

 ectoderm, and in them lie the nerves and excretory vessels (fig. 260). 



Some Nematodes live free in fresh or salt water, in soil, mud or decaying 

 vegetable matter, others parasitically in the most various organs of animals, 

 frequently also in plants. 



ANATOMY OF THE NEMATODES. 



All the Nematodes are covered by (i) a CUTICLE, which in the 

 small species is thin and delicate, while in the larger species it is 

 thickened, and may consist of several layers of complicated structure. 

 Canalicular pores do not occur. According to general opinion, 

 which is confirmed by the history of development, the cuticle is a 

 product of (2) the EPITHELIUM or ectoderm that had formerly existed 

 or is still found beneath it; in young specimens and small species it 

 is perceptible, but in older worms it frequently alters so considerably 



