EEPOET ON THE THNICATA. 
229 
The transverse vessels are large, and are pro^nded with slight horizontal membranes 
(PI. XXIX. fig. 14, tr.). 
The endostyle is conspicuous ; its course is very undulating (PL XXIX. fig. 15, en.). 
The nerve ganglion is large and almost globular in form. 
The alimentary canal forms a narrow loop. The oesophagus is a slightly curved 
funnel-shaped tube (PI. XXIX. fig. 15, oe.). The stomach is not large ; its anterior end is 
wider than the posterior, and the wall is folded longitudinally. The intestine extends for 
a considerable distance behind the stomach (PI. XXIX. fig. 15, i.), and then turns 
abruptly to the dorsal edge and anteriorly to pass into the long rectum which runs 
forwards along the dorsal edge of the abdomen and thorax (PI. XXIX. fig. 15, r.). 
The post-abdomen is variable in size. Some of those that lie detached in the lower 
part of the colony (PI. XXIX. fig. 13) are larger than those forming parts of the 
Ascidiozooids. Probably the separation of the post-abdomen from the remainder of the 
body is connected with a process of rejuvenescence in the colony, consisting in the 
death and expulsion of the older Ascidiozooids and the formation of new ones from the 
detached post-abdomens. There was, however, no evidence in the colony examined 
that the latter process had commenced. Kowalevsky has shown that in Amaroucium 
proliferum a process of gemmation, resulting in the formation of new Ascidiozooids in 
the old colony, takes place by the breaking up of the post-abdomen after its separation 
from the body of an old Ascidiozooid. 
A few large tailed larvae, with almost globular bodies and^two pigmented sense-organs 
placed close together, were found in the peribranchial ca^uties of some of the Ascidiozooids. 
This is one of those species in which the use of the post-abdomen as a distinguishing 
feature between Aplidium and Amaroucium might cause an error in classification. In 
some of the Ascidiozooids the post-abdomen is shorter than the combined thorax and 
abdomen, and, therefore, judging from this character alone, the species is an Aplidium. 
The shortness of the post-abdomen, however, is merely the result of gemmation having 
taken place, and the species really belongs, I consider, not to Aplidium but to Amaroucium 
(see p. 200). 
Amaroucium hepaticuin, n. sp. (PI. XXV. figs. 13, 14). 
The Colony was probably of moderate size and rounded in form. It is of a pale liver- 
colour, and is smooth externally. 
The Ascidiozooids are small, not more than 2 mm. in antero-posterior extent, and 
very narrow ; the body is not distinctly divided into regions. 
The Test is rather soft except on the outside of the colony, where it is distinctly 
firmer and tougher. It is of a pale grey tint internally, and becoming gradually darker, 
passes into a pale liver-coloured tint in the outer layer. It is almost opaque. The 
