644 



ENTOZOA. 



upon which they live, when their numbers become excessive, are well known ; and we 

 may mention, that the best remedy for those infesting the human intestines, appears 

 to be animal oil mixed with spirits of turpentine. 



The class admits of division into two orders, of which the organization is so dif- 

 ferent that they might, perhaps, be considered as two distinct classes ; or, at all events, 

 subclasses. These are, — Entozoa Nematoidea, or Cavitied Entozoa, which have the 

 intestine floating in a distinct abdominal cavity, and commencing at a mouth and ter- 

 minating at a vent ; and Entozoa Parenchymata, which have the viscera obscure, 

 generally in the form of vascular ramifications, and sometimes not at all discernible. 



THE FIRST ORDER OF THE ENTOZOA. 



Fig. 140. — Pentastoma tseuoldes. 



NEMATOIDEA. 



The members of this order have an external skin, more or less provided with muscular 

 fibres, and striated transversely. They have an intestinal canal running distinctly through 

 the whole length, and attached to the skin or tunic of the body by many filaments, which 

 appear to transmit nourishment. There is no circulation ; but, in some species, there are 

 two cords extending from a ring round the mouth, which are understood to be nerves. Re- 

 productive organs are apparent in all, and in some they are 

 greatly developed ; nor is the reproductive energy of the 

 animals under circumstances favourable to its developement 

 less active than the organs would indicate. This order forms 

 only one family, but contains several genera. 



Filaria (Thread-worm), — 

 Has the body long, slender, and thread-like, resembling that of the Gordii among Annelids, but 

 with mere marks on the body instead of the rings. The mouth is a circular opening at the anterior 

 extremity. They are not found in the open cavities, but are imbedded in the parenchyma of the 

 cellular tissues, between the coats of the viscera, and in other situations : they often exist in numerous 

 bundles, contained in a common cyst or tunic. They are not confined to the larger animals, but are 

 found in insects and their larvae, and even in various Mollusca. 



The most common, or at all events the most dreaded by Man, is the Guinea Worm, F. Medinensis. This trou- 

 blesome animal is very common in hot climates, where it insinuates itself under the skin, generally of the leg-, and 

 is said to gnaw to the length of ten feet, or more. According; to the accounts it will, if undisturbed, remain in the 

 body for a long; time without causing much uneasiness; but, if it is disturbed, it is said to cause the most excru- 

 ciating pain, especially if it finds its way to a very sensitive part of the body. When it shows itself externally, it is 

 extracted very slowly for fear of breaking it, as, if that takes place, its position in the body retreats more inwardly, 

 and causes great agony and convulsions. It is about the size of the tube of a Pigeon's quill, and has the tail ter- 

 minated by a sharp trunk. The sexes are in separate animals, but the mode of propagation is a little obscure. 



Trichocephalus, — 

 Have the body round, thread-like in the anterior part, and terminating in a round mouth ; and the 

 posterior part of the body is considerably thicker. 



T. dispar, is the most common species. It is from an inch to two inches in length, and thick for about the last 

 third. The thick part of the male is spirally convoluted, and the organ of generation is conspicuous. In the 

 female it is more straight, and has a simple opening. It is one of the worms of most frequent occurrence in the 

 human intestines ; and, in some diseases, it multiplies very rapidly. 



Trichovtoma, have the anterior part of the body tapering gradually to the mouth ; and Ori/uris, has the tail 

 slender and thread-like. One species of the latter, O. curvata, from an inch to three inches long, is found in the 

 coscum of the Horse. 



Cucullanus, has the body cylindrical, but thinner in the anterior portion. The head is blunt, and enveloped in 

 a sort of hood. This genus has hitherto been found in the intestines of Fishes only. One species, C. lacustris, is 

 common in the Perch, the Pike, and other Fishes. It is about an inch long* about the thickness of a thread, and 



