372 
MR. J. D. MACDONALD 
rests upon the nervous ganglion (fig. 2, e) ; and the blood-corpuscles may be always 
to pass above, but never beneath the latter. Many vascular trunks radiate from 
point ; thus one (fig 
directly backwards in the median line : from the fore 
part two channels (b b) diverge, passing forwards and outwards ; while several others pass 
outwards and upwards on either side (c), and two in particular {d d) from the upper sur- 
face enter the gill. Now, aU these vascular channels, according to their position and 
direction, become continuous with the subdivisions of those already described as arising 
from the heart, without any interposition of lacunae properly so called, and the scheme of 
circulation is thus completed. 
A superficial reticulation of vessels occurs between the muscular bands and the delicate 
membrane which immediately covers them, while the larger trunks evidently lie between 
The muscular coat is therefore very frequently per- 
the muscular ami branchial tunics 
forated by communicating canals ; so that an arrangement similar to that given in fi^ 
representing a portion of the ventral sinus with its contiguous vessels, is easily demon- 
strable, and affords a strong indication of a lining to the vascular system, though such has 
of late been very nearly denied to the Tunicata altogether, while it is admitted only in a 
limited sense in the Mollmca proper. (See Von Siebold and others.) 
EXPLANATION OF PLATE XXXV 
Fig. 1. Heart and great vessels of Peyea. a, visceral nucleus; b, chaplet of young; c, « eheoblast ;» 
d, heart ; e, gill band ; / & g, vessels arising from the anterior extremity of the heart ; h, en- 
dostyle ; ,, great vessel arising from the perivisceral sinus ; *, diverticula ; /, respiratory vessels ; 
m, mouth with lahi'nl frJA* & n 
sinus, a, ventral sinus ; b, antero-lateral trunks ; c c, lateral 
^ 1 • • • 
m, mouth with labial folds, &c. 
Nervo 
espiratory 
ficial plexus ; c, linear-extra- vascular space. 
perficial 
a, main trunk ; b b, super- 
