ENTOZOA. G59 



one on each side of the head ; infesting birds, fishes, and rep- 

 tiles. The species B. latus is common in the intestines of man, 

 in Switzerland, Russia, parts of France, &c. It is distinguished 

 from the Tania by the form of its segments, which are broader 

 than they are long, and by the openings of the ovaries, which are 

 beneath instead of at the sides. 



2. Tcenia, (Lat. a band.) This genus also has the body flat, long, 

 and articulated, but the articulations are so small and indistinct 

 for some distance from the head, (Plate XVI. fig. 9a,) that its 

 existence was for a long time unknown, and it was supposed the 

 worm obtained its nourishment through the lateral pores. The 

 head is round, with four suckers forming a square about the 

 mouth. 



The COMMON" TAPE WORM, T. solium, inhabits the human 

 intestines, but not with equal frequency in all countries. It is, 

 however, more widely distributed than the B. latus. The length 

 to which this worm attains is considerable, but it may be difficult 

 to assign its limit. Sometimes it is twenty feet and even more, 

 in length. One species, T. cateniformis, (Lat. chain-like,) about 

 an inch long, infests the cat. 



FIFTH SUB-ORDER. CYSTICA, (Gr. xtfcms, kustis, a bladder.) 



These worms are either flat or round, terminating behind in a 

 transparent cyst or bladder filled with a perfectly clear fluid ; 

 the head is retractile and provided with two or four pits, or four 

 suckers and a circle of small hooks, or with four unarmed ten- 

 tacles. This is the lowest group of the class, nothing is known 

 of its nutritive and some other organs. They are represented by 

 the Hydatida, or Hydatid, which consists of a globular bag, 

 composed of condensed albuminous matter, of a laminated or 

 plate-like texture, and containing a clear and colorless fluid. 



The young are developed between the layers of the parent 

 cyst, and thrown off internally or externally, according to the 

 species. Some have doubted whether it be an animal. Its struc- 

 ture resembles that of the lowest forms of Alga, or Sea-weed, 

 as the Red Snow, (Protoc&cus nivalis,) of the arctic regions. 

 Acephalocysts have been found in almost .every structure and 

 cavity of the human body. Some species live in the brain and 

 spinal cord of sheep, and in the brain of oxen, giving rise to the 

 disease called " staggers." 



