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NEMA THELMINTHES 



CLASS 1. 

 ORDER I. NEMATODA. 



Definition. — ^Nemathelminthes with white fiHform bodies, with 

 usually a complete alimentary canal in the adults, but sometimes 

 this may be represented by only an oesophagus and a rudimentary 

 intestine; with papillae on the head. The male with one testis, a 

 strongly recurved posterior extremity, and usually spicules. The 

 female with a vulvar opening always distinct from the anus. Egg 

 contains ovum only. 



Morphology.— The Nematoda are parasitic, as a rule, but 

 minute sexually mature forms can be met with in moist soil all over 

 the world. The body is enclosed in a thick, transparent, smooth, 

 or ringed cuticle, which may form hooks, spines, or lateral fins. 



Under the cuticle comes a syncytium called the epidermis, under 

 which is the peculiar muscular layer cut into four quadrants by 

 thickenings of the epidermis, which project inwards, surrounding 

 dorsally and ventrally a nerve cord, and laterally excretory canals. 

 Under the skin comes the large undivided body cavity, which is not 

 of the nature of a true coelom, as it is not between the two layers 

 of the mesoblast, but between mesoblast externally and hypoblast 

 internally, and contains a fluid which may represent the hsemolymph 

 fluids of higher animals. 



The digestive system consists of a mouth situated at the anterior 

 end, and surrounded by two to six lips, which opens into a thick 

 suctorial oesophagus lined with chitin. 



The oesophagus opens into the intestine, which is a thin-walled 

 tube lined by a simple layer of endothelial cells, and leads to the 

 short chitinous rectum, which ends in the anus. 



The excretory system consists of two longitudinal tubes lying in 

 the lateral line, and uniting anteriorly by a transverse ' bridge ' to 

 open in a pore situated in the mid-ventral line just behind the mouth 

 in the region of the nerve ring. 



The nervous system consists of a circumoesophageal ring, with six 

 anterior and six posterior nerve trunks. 



The sexes are separate. The male reproductive organs consist 

 of one tube divisible into testis, vas deferens, vesicula seminalis, 

 and ductus ejaculatorius, which opens on the ventral surface of the 

 rectum close to the anus, while the posterior end of the body is 

 modified J for sexual purpose with alse and papillae. The female 

 reproductive organs consist of two much-coiled tubes divisible into 

 ovary, oviduct, and uterus, which join together to form the simple 

 vagina, which opens about the middle of the body in the mid-ventral 

 line; in some instances just in front of the anus, in others, as in the 

 filaria worms, quite near the head. 



Biology. — -They appear to live upon the juices of the part of the 

 body in which they are found. Generally this is the intestine, the 

 contents of which supply them with ample food. But some of them 

 are capable of entering the villi of the intestine. 



