504 ENTOZOA. 



floating in a distinct abdominal cavity, a mouth, &c., and the Ento- 

 zoa Parenchymata, where the parenchyma of the body contains 

 obscurely terminated viscera, most commonly resembling vascular 

 ramifications, and sometimes not visible. 



ORDER I. 



NEMATOIDEA, Rud. 



This order comprises those whose external skin, more or less 

 furnished with muscular fibres, and usually striated transversely, 

 contains an abdominal cavity in which is a distinct intestinal canal, 

 extending from the mouth to the extremity, and where the sexes are 

 usually distinct. The intestine is connected with the neighbouring 

 parts and the general envelope of the body by numerous threads, 

 considered by some writers as vessels for the conveyance of the 

 nutritious fluid, and by others as trachea, but without any proof of 

 the fact. It is impossible to detect any true circulation in these 

 animals, but in several there appear to be one or two nervous cords 

 arising from a ring which surrounds the mouth, and extending the 

 whole length of the body along the internal surface of the envelope. 



FILARIA, Lin. 



Where the body is elongated, slender, filiform, and perforated at the ante- 

 rior extremity by a round oral aperture. The Filariae in their external ap- 

 pearance are very similar to the Gordii. They are chiefly found in those 

 cavities of animals which do not open externally, such as the cellular mem- 

 brane, and even in the thickness of the membranes and the parenchyma of 

 the viscera ; there we sometimes find them in bundles and countless num- 

 bers, enveloped in species of capsules. They are found in Insects and their 

 larvae, and even in the visceral cavity of several Mollusca. The most cele- 

 brated species of this genus 



F. medinensis, Gm., (the Guinea Worm), is very common in hot cli- 

 mates, insinuates itself under the skin of man, generally that of the leg, 

 where, if credence be given to the reports of certain authors, it acquires a 

 length of ten feet and more. It is about as thick as the barrel of a Pigeon's 

 quill. Its pointed and hooked tail constitutes its distinguishing character. 



TRICHOCEPHALUS. 

 Where the body is round, thickest posteriorly, and as slender as .a thread 



