166 CLASS V. 



structure of its intestinal canal as well as in other respects. On that 

 account CUVIER and OWEN have with propriety removed it from this 

 division in which RUDOLPHI placed it. The intestinal canal lies in 

 a free cavity of the body, though covered by the coils of the oviduct, 

 and ends with a distinct anus l . The position and form of the canal 

 agrees with the same in the Round-worms; only in the oesophagus 

 is there some difference, since this tube in the Nemato'idea runs 

 from the mouth at the anterior extremity of the body backwards in 

 the same plane with the intestinal canal, whilst in Pentastoma it 

 ascends obliquely because the mouth is situated on the abdominal 

 surface. In the Nemato'idea the oesophagus is muscular, and in 

 many species wider at its termination. The intestinal canal that 

 succeeds it is straight, and its whole course continues nearly of the 

 same width. In Ascaris lumbrico'ides pedunculated pyriform vesicles 

 are found, which adhere to the internal surface of the integument, 

 and occupy the space between the skin and the intestinal canal. 



A vascular system has been discovered in many entozoa. 

 [Amongst the Nemato'idea BLANCH ARD has described in Ascaris 

 megalocepliala CLOQUET two longitudinal vessels lodged in each of 

 the lateral canals within the integument, which extend from one 

 extremity of the body to the other. At about the depth of one 

 third of the oesophagus, the two, supposed to be arteries, leave their 

 tubes to form an arch behind the oesophagus ; on the arch a small 

 ampulla is seen which is supposed to supply the office of a heart. 

 The two arteries descend in the tubes throughout the whole length 

 of the body, and communicate with the two other longitudinal 

 vessels supposed to be veins 2 . In the tcenia the longitudinal canals, 

 four or six in number, communicate by transverse branches, and 

 open in the last joint into a pulsatile vesicle, which expels their 

 contents in drops at intervals. In the suctorial worms the fine 

 vascular network, hitherto considered to be a circulating system, 

 has been shewn by VAN BENEDEN to be an appendage of the 

 tubular system, which terminates in a vesicle that opens externally 

 by & foramen caudale. The apparatus in the last two families of 



1 See OWEN Transact. Zool. Soc. I. 1835, PI. 41, fig. 12 ; DIESING Ann. des Wiener 

 Museums, I. 1836, Tab. n. fig. 2 ; comp. Tab. I. fig. 20, of Pentastoma proboscideum. 



2 BLANCHAKD Ann. des c. nat. 30 Sdvie, Zool. Vol. xi. pp. 146, [47, and CUVIER 

 R. Anlni. e"dit. illus. Zooph. PI. 26, fig. i c. 



