316 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
The second canal is the pseudhamal (Pl. IIL., fig. 28 ; 
Pl. TV., figs. 29, 30, and 33, 7.p.h.c.).. Tie iimee ene 
the inner, axial face of the nerve trunk, and, like the 
epineural canal, ends blindly at the apex of the test. It 
also does not communicate with the corresponding circular 
pseudhemal vessel (Pl. III., fig. 28, epdiey ihe 
pseudhemal canals contain a fluid similar to that found 
in the coelom, and it is possible that their function may 
be the nourishment of the nerve trunks, with which they 
are so intimately associated. They give off lateral branches, 
which run parallel with those of the water-vascular canal 
and of the radial nerve. 
Little is known concerning the ontogenetic history of 
the pseudhzemal system. The corresponding system in 
the Holothuroidea has a definite epithelial lning, which 
points to the conclusion that it 1s derived from the hydro- 
enterocel, and throws doubt upon the schizoccelomic 
origin which has been claimed for it in the starfishes. 
The blood-vascular system of Hchinus and its allies has 
been the subject of much discussion, and the descriptions 
published by Teuscher, Hoffmann, Ludwig, Hamann, 
Cuénot, Perrier, and Koehler, differ considerably in detail. 
There are undoubtedly two vessels, which run alongside 
the inferior coil of the intestine, in the mesentery which 
supports the latter. One—the ventral vessel (Pl. IIL., fig. 
23, v.v.).—runs along the inner axial side of the intestine 
and is connected by numerous lacunee with the dorsal vessel 
(Pl. V., fig. 37, d.v.), which runs on the outer side of 
the intestine. Both vessels have been described as open- 
ing into a circular vessel, which is said to surround the 
cesophagus in close proximity to, yet quite distinct from, 
the water-vascular ring-canal. The existence of such a 
separate circular vessel is, however, open to doubt; and 
this remark applies with greater force to the blood-vessels 
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