132 



ENTOZOA. 



tured vessels, the head of the Tape-worm is 

 the sole natural instrument by which it im- 

 bibes its nutriment, and it is to the expulsion 

 of this part that the attention of the physician 

 should be principally directed, in his attempts 

 to relieve a patient from these exhausting para- 

 sites. 



Trematoda. Four kinds of vessels or canals 

 are met with in the parenchymatous body of the 

 Trematode worms, viz. digestive, nutritive or 

 sanguiferous, seminal, and ovigerous. In the 

 genus Monostoma, the digestive canal is bifur- 

 cated, each branch traverses in a serpentine 

 direction the sides of the body, and they are 

 united, in some species, by a transverse com- 

 municating vessel at the caudal extremity ; in 

 others, as Monost. mutabile, they converge and 

 terminate in an arched vessel at the posterior 

 part of the body. They are of small size, and 

 not very clearly distinguishable from the sangui- 

 ferous vessels. 



In the Distoma hepaticum, the digestive 

 organs are more distinctly developed. The 

 oesophagus is continued from the anterior pore, 

 and forms a short wide tube, shaped like an 

 inverted funnel. Two intestinal canals are 

 continued from its apex, which immediately 

 begin to send off from their outer sides short 

 and wide coacal processes, and continue thus 

 ramifying to the opposite end of the body, 

 but have no anal outlet. Rudolphi* states 

 that when successfully injected with mercury, 

 more minute vessels are continued from the 

 apices of the digestive canals, which form a net- 

 work over the superficies of the body. A similar 

 dendritic form of the digestive canal obtains in 

 the singular genus Diplozoon, discovered by 

 Nordmann in the gills of the Bream; the central 

 canal and ramified ccecal processes in this En- 

 tozoon are represented (Jig. 328, vol.i. p. 654,) 

 on that moiety, which is opposite the left hand 

 of the observer : on the other moiety the vascu- 

 lar system alone is delineated. The latter is not, 

 like the digestive canal, common to both halves 

 of the body, but consists of two closed systems 

 of vessels, each peculiar to its own moiety. 

 Two principal trunks, a, a, traverse the sides 

 of each moiety, preserving a uniform diameter 

 throughout their entire course. In the external 

 vessels marked a, a, Nordmann states that 

 the blood is conveyed forwards or towards the 

 head: in the internal ones, it passes back- 

 wards in the opposite direction. The latter 

 vessels commence by many minute branches 

 which unite in the space between the oral 

 suckers and the anterior extremity of the 

 body, and terminate between the disc and 

 suckers at the posterior extremity of the body. 

 The exterior or ascending vessels begin where 

 these disappear and pass towards the opposite 

 end of the body : both trunks freely inter- 

 communicate by means of superficial capil- 

 laries. The blood moves through them with 

 great rapidity, but without being influenced 

 by any contraction or dilatation of the vessels 

 themselves. The circulation continues for 

 three or four hours to go on uninterruptedly in 



* Entoz. Synopsis, p. 583. 



each moiety of the Diplozoon, after they have 

 been separated from one another by a division 

 of the connecting band. The blood itself is per- 

 fectly limpid. It should be observed, with refe- 

 rence to the above description, that the appear- 

 ance of circulatory movements in the vessels of 

 the Diplozoon paradoxum is ascribed by Ehren- 

 berg ( Weigmann's Archiven, 1835, th. ii.) and 

 Siebold ( Ibid. 1836, th. ii.) to the motion of 

 cilia on the inner surface of the vascular canals. 



In the genus Diplostomum, in which the 

 nutritious and vascular systems characteristic 

 of the Trematoda are peculiarly well displayed, 

 (fig. 81,) a short and slightly dilated canal is 

 continued from the mouth, and soon divides 

 into two alimentary passages or intestines, e, e, 

 which diverge, and proceed in a slightly un- 

 dulating course, towards the hinder sacciform 

 appendage of the body, dilating as they de- 

 scend, and ultimately terminating each in a 

 blind extremity,/,/. The contents of this long 

 bifid blind alimentary canal are of a yellowish 

 brown colour, especially in old individuals, 

 and consist of a finely granular substance. 

 As there is no separate anal aperture, the crude 

 and effete particles are probably regurgitated 

 and cast out by the mouth, as in all other 

 Trematoda. 



The posterior projection of the body, g, 

 Nordmann compares to the posterior appen- 

 dage in the Cercarue ; it is terminated by a 

 posterior aperture which seems to be the ex- 

 cretory outlet of some secerning organ ; since 

 a milky fluid is sometimes ejected from it 

 with force. In a species of Distoma (Distoma 

 clavatum, Rud.) which I recently dissected, 



Fig. 81. 



Digestive and nutrient canals, Diplostomum volvens, 

 magnified. 



