ENTOZOA. 



121 



four mouths, or oscula, are situated on the 

 anterior surface, (a, Jig. 63,) and surround 

 the central rostellum, which is very short, termi- 

 nated by a minute apical papilla, and surround- 

 ed by a double circle of small recurved hooks. 

 The segments of the neck, or anterior part of the 

 body, are represented by transverse rugae, the 

 marginal angles of which scarcely project be- 

 yond the lateral line; the succeeding seg- 

 ments are subquadrate, their length scarcely 

 exceeding their breadth, they then become sen- 

 sibly longer, narrower anteriorly, thicker and 

 broader at the posterior margin, which slightly 

 overlaps the succeeding joint ; the last series of 

 segments are sometimes twice or three times as 

 long as they are broad. The generative orifices 

 (b, 6) are placed near the middle of one of the 

 margins of each joint, and are generally alter- 

 nate. 



The T&nia solium is subject to many varieties 

 of form or malformations; the head has been ob- 

 served to present six oscula instead of four. In 

 the Imperial Museum at Vienna, so celebrated 

 for its entozoological collection, there is a por- 

 tion of a T<enia solium, of which one of the 

 margins is single and the other double, as it 

 were two taeniae joined by one margin. In the 

 Museum of the College of Surgeons is preserved 

 a fragment of the Taenia solium of unusual size; 

 it swells out suddenly to the breadth of three- 

 fourths of an inch with a proportionate degree 

 of thickness, and then diminishes to the usual 

 breadth.* 



The species of Taenia infesting the intestines 

 of other animals are extremely numerous, ne- 

 vertheless they are rare in Fishes, in which they 

 seem to be replaced by the Eothriocephali and 

 Ligula. The determination oLthe species in 

 this, as in every other natural ana circumscribed 

 genus, is extremely difficult and often uncer- 

 tain : their study is facilitated by distributing 

 them into the three following sections, of which 

 the first includes those species which are de- 

 prived of a proboscis, T<eni< inermes ; the 

 second those which have a proboscis, but un- 

 armed, T&nia rostellata; the 



Fig. 64. third the Tape-worms with an 

 uncinated proboscis, T <eni<e ar- 



Distoma hepa- 

 ticum, twice 

 natural size. 



same locality. The form of this species of En- 

 tozoa is ovate, elongate, flattened ; the anterior 

 pore or true mouth (a) is round and small, the 

 posterior cavity (6), which is imperforate and 

 subservient only to adhesion and locomotion, 

 is large, transversely oval, and situated on the 

 ventral surface of the body in the anterior 

 moiety. Between these cavities there is a third 

 orifice (c) exclusively destined, like the orifice 

 on each joint of the Taenia, to the generative 

 system; and from which a small cylindrical 

 process, or lemniscus, is generally protruded in 

 the full-sized specimens. 



The form of the body is so different in the 

 young Distomata, that Rudolphi was induced 

 to believe the specimens from the human gall- 

 bladder which were in this state, to belong to 

 a distinct species, which he termed lanceo- 

 latum ; this modification, which is wholly de- 

 pendent upon age, is shown in the subjoined 

 figure; and we shall hereafter have to notice the 

 more extraordinary changes, amounting to a 

 metamorphosis, which the Distomata infesting 

 the intestines of Fish undergo. 



The Polystoma Pinguicola was discovered 

 by Treutler, in the cavity of an indurated adi- 

 pose tubercle, in the left ovarium of a female, 

 aetat. 20 ; it is represented in situ, at A,/g. 62. 

 Its natural size and shape 

 is shewn at B, the body is 

 depressed,subconvexabove, 

 concave below, subtruncate 

 anteriorly, a little contracted 

 behind the head, pointed at 

 the posterior extremity. On 

 the under side of the head 

 C, there are six orbicular 

 pores disposed in a semi- 

 lunar form : a larger sucto- 

 rious cavity occurs on the 

 ventral aspect at the begin- 

 ning of the tail (b B), and a 

 small orifice is situated at 

 the apical extremity. 



A second species of Po- 

 lystoma (Polystoma Vena- 

 rum), stated by Treutler to 

 have been situated in the 

 anterior tibial vein of a Man, 



The Trematode Order, which 

 is the most extensive division of 

 the Parenchymatous class of En- 

 tozoa, and embraces the greatest 

 number of generic forms, in- 

 cludes only two species infesting 

 the human body, one of which, 

 the liver-fluke (Distoma hepati- 

 cum), is extremely rare, and the 

 other (Polystoma Pinguicola) 

 somewhat problematical. 



The Distoma hepaticum (Jig. 

 64) is found in the gall-bladder 

 and ducts of the liver of a variety 

 of quadrupeds, and very com- 

 monly in the Sheep. When it 

 occurs in the Human species, it 

 is generally developed in the 



Polystoma 

 Pinguicola. 



* See Catal. of Nat. Hist. No. 216. 



which was accidentally ruptured while bathing, 

 is generally supposed to have belonged to a 

 species of Planaria, and to have been acci- 

 dentally introduced into the strange locality 

 above-mentioned. 



The worms of the Trematode order are those 

 which are most frequent in the interior of the 

 eyes of different animals, perhaps the most 

 singular situation in which Entozoa have as yet 

 been found, and respecting which much in- 

 teresting information has recently been given 

 by Dr. Nordmann, in the first part of his 

 beautiful work entitled " Mikrographische 

 Beitrage zur Naturgeschicte der Wirbellosen 

 Thiere." Of the species described and figured 

 in that work, we have selected for illustration 

 the Diplostomurn volvens. 



Fig. 66 exhibits a magnified view of the 

 vitreous humour of a Perch ( Percafluviatilis, 

 Linn.) containing numerous specimens of this 



