PARENCHYMATA. 649 



DiBATHRYORHYNCHUS, 



Have two little probosci, or tentacula, on the head, bristled with small hooks. 



Flaviceps, — 

 Have four tentacula, with curved spines, with which they penetrate the substance of animals. Some 

 have the body retractile into a membrane, and others not. One, which infests the Skate family, is 

 several inches long, and has the head shaped like a flower. 



Tetrarhynchus, — 

 Resembles the head and the first two joints of the preceding. One species of it infests the tongue of 

 the Turbot. Tentacularia differ only in wanting the spines on the tentacula. 



Those which have the head with four suckers, but the body terminating in a sort of bladder, and 

 the joints very obscure, are also with propriety separated from the true Tape-worms. 



Cysticercus, — 

 Or Hydatids, have the bladder supporting one body and head. They are very numerous, and found in 

 the membranous and cellular substances of many animals. They are very common in Ruminants, and 

 many other Mammalia, as in the Hare, the Rabbit, the Hog, various species of the Quadrumana, and 

 even in Man. 



One species, C. ceUulosa, occurs in vast numbers among the muscular fibres of the Hog, and produces, or 

 accompanies, the disease in that animal which is known by the name of the Measles, and renders tlie flesh both 

 xnipalatable and unwholesome. It is small, breeds rapidly, and finds its way to all parts of the body, even to the 

 heart and the eyes. It is said, however, that they have never been found in the Wild Boar, which proves that 

 they, or the disease which favours their developement, are induced by the very artificial manner in which tame 

 Hogs are bred. Those found in the Quadrumana and in Man are very analogous. Acrostoma, found in the 

 amnios of the Cow, is very nearly allied. 



C(eimrus, have several bodies and beads attached to the same bladder. C cerebralis, is well known as infecting 

 the brain of the Sheep, consuming the substance, and occasioning the disease called the " staggers," in which the 

 animal totters round and round toward the affected side, but without any alleviation of its suffering. Other 

 species infest the Ox and other ruminants, and they all produce the same sort of effect ; but, as scarcely any 

 ruminant is so susceptible of change by artificial means as the Sheep, they are most severe upon it. In some 

 instances the bladder is as large as an egg, with thin walls, susceptible of contraction ; but the bodies and heads 

 are small, and can be almost entirely withdrawn into it. 



ScoLEX, Linn. 

 Tlie body round, contracted to a point posteriorly, and have a variable head, with two or four suckers. 

 The inflated part is very contractile. Most of the species are small, and live on fishes. 



THE FOURTH FAMILY OF THE PARENCHYMATA,— 

 The Cestoidea, — 

 Comprises those which are destitute of external suckers. This consists of only a single genus, — 



LiGULA. 



These are the simplest in their organization of all the Entozoa. The body is like a long, flat ribbon, 

 with one longitudinal stria, and numerous cross ones ; and the internal parenchyma appears to contain 

 nothing but the ova distributed through its substance. They are chiefly found in the abdomen of birds 

 and fresh-water fishes, whose bowels they envelope and contract in such a manner as to destroy them; 

 and at certain periods they perforate the abdomen, and leave it. 



One species, L. abdominalis, infests the Bream ; and, in some parts of Italy, it is considered agreeable food. 



[It will be perceived that the whole of the Entozoa are remarkal)le for the great developement of 

 their reproductive system ; and not a few of them for the great and rapid growth of the individual ; 

 and this is exactly what analogy would lead us to suppose. Living, not only in the bodies, but upon 

 the living, or already assimilated substance of other animals, the labours which they have to perform are 

 few and simple, compared with those of most of the animal creation. They have but little use eitlier 

 for locomotion or sensation ; and they have probably less for circulation, respiration, or digestion, 

 excepting in the Planarii and any others which do not live in the bodies of other animals. As their 

 habitations are obscure, their habits are equally so ; and the purpose which they answer in the economy 

 of nature is quite a mystery.] 



