100 
THE VOYAGE OE H.M.S. CHALLENGER. 
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Alimentary Canal . — The abdominal part of the alimentary canal is very opaque^ 
being of a dark indigo-blue colour. This gives the colony its peculiar tint, and it is 
caused by the blood-corpuscles, which are nearly black, being collected into small clumps 
which fill the large sinuses extending through the mantle. 
The oesophageal opening, placed at the posterior end of the branchial sac, near the 
dorsal margin, is of large size, and has the edge and its inner surface for a short distance 
down thrown into a remarkable series of folds, presenting curiously complicated ridges 
and tooth-like processes (PI. XII. fig. 4). The oesophagus is short and wide, and opens 
into the slightly larger stomach, which is continued without much diminution in size 
into the intestine, the first portion of which forms with the stomach and oesophagus a 
slightly curved antero-posterior line. The intestine having reached the posterior end 
of the abdomen, turns sharply round and runs forward parallel to the stomach; then 
curving upwards, crosses the anterior part of the oesophagus, and after a short rectal 
course through the peribranchial cavity, ends in a rather prominent anus, the margin of 
which is disposed in a series of regular folds (PI. XII. fig. 4). The stomach is not 
plicated, and there is no typhlosole in the intestine (PL XII. fig. 8). 
Vascular System . — The heart is placed on the right side of the body in the abdominal 
region, and lies in the elongated space between the stomach and the intestine. It is a 
long fusiform undulating tube with very thin walls, which are seen under a high power 
to contain closely placed transverse fibres which sometimes exhibit a fine cross striation^ 
and are circular in section. Outside this muscular coat is a thin layer of connective 
tissue, consisting of a delicate membrane in which fusiform and branched corpuscles are 
imbedded. 
Reproductive Organs. — The genital glands are situated on the left side of the 
abdomen (PI. XII. fig. 6), to which they are more closely applied than in the last 
species. In this case the male organs greatly predominate. A large number of oval or 
pyriform pale yellow vesicles with granular contents are scattered over the surface of the 
intestine. These are the sperm aria or testes. They are in connection with short and fine 
ducts which unite into about a dozen larger ones, and these converge towards and open 
into the lower end of a large opaque yellowish-brown vas deferens, which runs up the 
inner edge of the intestine towards the atrium (PI. XII. figs. 6, 7). 
Usually in the adult Ascidiozooid no ovary is visible (PI. XII. fig. 6). Earely one or 
two large ova are seen among the testes, and more frequently one, two, or three mature 
ova are found occupying different positions on their way to the atrium (PL XII. fig. 6). 
In young Ascidiozooids, however, from the base of the colony (see p. 96), the ovary is 
well developed, and exactly resembles that of the last species (see PL XII. fig. 8). These 
circumstances seem to indicate the existence of protogyny, each Ascidiozooid being first 
female and then male, and the ova of those near the base being fertilised by the 
spermatozoa of the older ones farther up the colony. An Ascidiozooid such as the one 
