648 ENTOZOA. 



Jji.^-itfiu/astrr, sliould bpst occupy this place in tlie system. It Las the under-side formed into iirnjectiiifi; laniiriEe 

 h\ fuur rows uf little furrows. One small species, found on Mus^^els. 



Planatha. 



This genus, tliough not inlialntants of the inlcrior of other animals, hut of the waters, are yet so 

 simihir to the Flukes in appearance and organisation, tliat this was the hest station for tliem. Some 

 inhabit fresh water and others salt. 



Their body is depressed, parenehymatous, 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 ramifieil vessels. They are bisexual, and in their manner 

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

 structure uf 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 re])roduced, and a partial division of the 

 body will even jiroduce an animal with two lieails or two tails, according as the anterior or posterior 

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

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



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

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



THE THIRD FAMILY OF THE PAREXCHYMATA,— 



Tjinioidca (The Tape-worm Family). 

 This family includes all the Intestinal ^Vorms wliich have two or four suckers on the head. The 

 space lietween 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. 



T.EN'IA,— 



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

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

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

 bead, 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, somelimes siniple and sonietinie^ rauiitied. The Tajic-worms are amung the must cruel enemies 

 of those animals in \\hich they breed, as they completely ab--urb their nourishment and exhaust their 

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



Tania lata, or Ttrnia vulgaris, the Common Tape-worm, which has the joints broad and flat, with a double 

 port- 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 len^rtli is about an inch broad ; but the portion toward the head 

 is considrraldy narro\\rr. They are exceedini;ly annnying, and so tenacious of their hold tliat the most violent 

 remedi*.'s aie t-nnictinies unable to exjiel them. 



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



Ttctiia 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 ]ong;er than in the Common Tape-worm, and they have the pores alter- 

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

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

 the same time is a vult;ar 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 dilTerent. 



Tricuspidaria, — 

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

 spines. 



Oidy one species, T. nodulusa, is known. It infests the Perch, the Pike, and various other tishes. 



POTHRYOCEPIIALUS, 



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

 some bbds. 



