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 Rupotpnt placed it. The intestinal canal les in 
a free cavity of the body, though covered by the coils of the oviduct, 
and ends with a distinct anus!. The position and form of the canal 
agrees with the same in the Rownd-worms; only in the cesophagus 
is there some difference, since this tube in the Nematoidea runs 
from the mouth at the anterior extremity of the body backwards in 
the same plane with the intestinal canal, whilst im Pentastoma it 
ascends obliquely because the mouth is situated on the abdominal 
surface. In the Nematoidea the cesophagus 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 lumbricoides 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 Nematoidea BLANCHARD has described in Ascaris 
megalocephala 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 cesophagus, the two, supposed to be arteries, leave their 
tubes to form an arch behind the cesophagus; 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®. In the éenda 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 m a vesicle that opens externally 
by a foramen caudale. The apparatus in the last two families of 
1 See OWEN Transact. Zool. Soc. 1. 1835, Pl. 41, fig. 12; Drestne Ann. des Wiener 
Museums, 1. 1836, Tab. 11. fig. 2; comp. Tab. 1. fig. 20, of Pentastoma proboscideum. 
* BLANCHARD Ann. des Sc. nat. 3e Série, Zool. Vol. Xt. pp. 146, 147, and CUVIER 
R. Anim. édit. illus. Zooph, Pl. 26, fig. ve. ; 
