648 



ENTOZOA. 



Apsidogaster, should best occupy this place in the system. It has the under-side formed into projecting laminse 

 by four rows of little furrows. One small species, found on Mussels. 



Planaria. 



This genus, though not inhabitants of the interior of other animals, but of the waters, are yet so 

 similar to the Flukes in appearance and organisation, that this was the best station for them. Some 

 inhabit fresh water and others salt. 



Their body is depressed, parenchymatous, and has no distinct abdominal cavity. The mouth, 

 which is in the middle of the lower part of the body, or a little nearer the tail, is, as in the Fluke, 

 dilated into a sort of proboscis, and leads to ramified vessels. They are bisexual, and in their manner 

 of reproduction have very much similarity to the Flukes, and they appear also to be similar in the 

 structure of their eyes. They are exceedingly voracious, and will even feed upon their own species. 

 They multiply rapidly in the ordinary way, and also by division of the body — even spontaneous divi- 

 sion, as is alleged. Mutilated parts are also very readily reproduced, and a partial division of the 

 body will even produce an animal with two heads or two tails, according as the anterior or posterior 

 end is cleft. Several species inhabit the fresh waters ; but larger ones are met with on the sea-shores. 

 [Their appendages vary ; but it is not easy to say what is specific and what accidental.] 



M. Duges separates from the true Planaria, Prostoma, which have an opening at each end of the 

 body ; and Derastoma, in which there is one opening, nearer the anterior than in Planaria. 



THE THIRD FAMILY OF THE PARENCIIYMATA,— 



T.£nioidea (The Tape-worm Family). 



This family includes all the Intestinal Worms which have two or four suckers on the head. The 

 space between these is, in some cases, marked by a pore ; and in others, drawn out into a sort of pro- 

 boscis, naked, or armed with spines. In some instances, there are four little probosci armed in this 



manner. 



Tjenia, — 



The Tape-worms, commonly so called, form the most numerous genus, and are, unfortunately, but too 

 well known. They have the body long — often exceedingly so, flat, and composed of a number of 

 joints, or articulations, more or less marked ; they are thinner anteriorly, and generally have a square 

 head, with four small suckers. Some have thought that they have discovered canals ramifying from 

 the suckers, and winding along the joints of the body. Each joint has two pores, differently situated 

 in the different species, which appear to be the orifices of ovaries, situated in the thick parts of the 

 joints, sometimes simple and sometimes ramified. The Tape-worms are among the most cruel enemies 

 of those animals in which they breed, as they completely absorb their nourishment and exhaust their 

 substance. Some have no projecting part among the four suckers. Among these is 



T<enia lata, or Tania vulgaris, the Common Tape-worm, which has the joints broad and fiat, with a double 

 pore in the middle of each flat side. They are often twenty feet long-, and specimens of more than a hundred feet 

 have been observed. The principal part of the length is about an inch broad ; but the portion toward the head 

 is considerably narrower. They are exceedingly annoying, and so tenacious of their hold that the most violent 

 remedies are sometimes unable to expel them. 



Other species have the prominence between the suckers, but with little radiating points. Of these, 



Taenia solium, the Solitary Worm, is one of the most annoying to the human species. The joints, with the 

 exception of those in the anterior part, are longer than in the Common Tape-worm, and they have the pores alter- 

 nately on the opposite sides. The most common length is four or five feet ; but much longer ones are some- 

 times met with. The detached joints are called cucurbitini. That only one can exist in one human body at 

 the same time is a vulgar error. Of all Intestinal Worms, they are the most dangerous, and the most difficult 

 to expel. 



Several genera, or subgenera, are distinguished from the true Taenia by the form of the head, and others by a 

 vesicle at the termination of the body. About five genera have the head different. 



Tricuspidaria, — 

 Have the head formed into tubes, and each side has, instead of a sucker, three very sharp-pointed 

 spines. 

 Only one species, T. nodulosa, is known. It infests the Perch, the Pike, and various other fishes. 



BOTHRYOCEPHALUS, 



Have two longitudinal grooves on the head instead of suckers. They infest various fishes, and 

 some birds. 





