NEMATOIDEA. 505 



anteriorly. This slender partis terminated by a round mouth. The most 

 common species is the 



T. dispar, Rud. From one to two inches in length, of which the thickest 

 portion forms but the third. This part, in the male, is convoluted spirally. 



It is one of the most common Worms in the great intestines of Man, where, 

 in certain diseases, it becomes prodigiously multiplied. 



CUCULLANUS. 



Here the body is round, and most slender posteriorly. The head is obtuse 

 and invested with a sort of hood that is frequently striated; the mouth is 

 round. 



They have hitherto been found in Fish only. The most common species 

 is that which inhabits the Perch and also infests the Pike, &c. 1% is vivipar- 

 ous, about an inch long, as thick as a thread, and of a red colour, owing to 

 the blood with which its intestine is usually filled. 



OPHIOSTOMA. 



The same kind of body as the preceding, but distinguished by a trans- 

 versely cleft mouth, and consequently furnished with two lips. 



ASCAEIS, Lin.(l) 



The Ascarides have a round body, attenuated at each extremity, and a 

 mouth furnished with three fleshy papills, between which an extremely 

 short tube occasionally projects. This genus is very numerous in species 

 which are found in all kinds of animals. 



Two white threads, one of which extends along the back, and the other 

 along the abdomen, are considered by Messrs Otto and Cloquet as the ner- 

 vous system of these animals; two other and thicker threads, one on the 

 right and the other on the left, are considered by some as muscular, and by 

 others as vascular, or even as tracheae. 



In some, the head is destitute of lateral membranes. The most common 

 species, the 



A. lumbricoides, L., is found without any essential difference in Man, the 

 Horse, Ass, Zebra, Hemiona, Ox and Hog. It has been seen more than fif- 

 teen inches in length. Its natural colour is white. 



Other species are furnished with a little membrane on each side of the 

 head. Such is 



Jl. vermicularis, L. Very common in children. It is not more than five 

 lines in length, and is thickest anteriorly. 



(1) tta-KApK, the name of the small species that is found in Man, is derived 

 from cur*f i, to leap, to move. 



3 O 



