REPORT ON THE THNICATA. 
175 
forms. A few small ova may be found near its upper end in some Ascidiozooids, but 
tbe greater part of it is occupied by a mass of young and undeveloped spermatic 
vesicles. Tbe vas deferens is not conspicuous, but may generally be made out running 
through the upper part of the post-abdomen and continued forwards alongside tlie 
rectum. No larvm were found in any of the Ascidiozooids examined. 
The posterior end of the post-abdomen (PL XXIV. fig. 4) forms a slightly swollen clear- 
walled bulb in which the heart lies, and it presents terminally a small knob whicli 
resembles a very rudimentary vascular appendage. The double septum traversing the 
post-abdomen is more con.spicuous than usual (PI. XXIY. fig. 4, p.ah.), and transverse 
sections show that its lumen is complicated and that its walls are formed in most places 
of large columnar cells (PL XXIV. fig. 8). The figure shows the ectoderm externally 
formed of squamous cells (ec.), and enclosing a great mass of rounded mesoderm cells 
(mes.) in which two cavities (coel.) occur, one on each side of the median double 
septum, which is formed of columnar endoderm cells [end.) bounding a narrow lumen 
(ar.), which is, according to Kowalevsky, a prolongation of the posterior end of the 
branchial sac. 
Atopogaster elongata, var. pallida, nov. (PL XXIV. figs. 9, 10). 
The Colony is an irregular mass growing upwards from a broad base of attachment. 
It is rather elongated from the base upwards, and tapers slightly. The upper end is 
blunt. The colour is a pale oj^aque grey. The surface is very uneven, being cut up by 
deep grooves and ridges. 
The length is 6'5 cm., the greatest breadth (above the base) is 3 cm., and the usual 
thickness is 2 cm. 
The Ascidiozooids are small but very numerous, and are arranged quite irregularly. 
Their anterior ends are more opaque than the surrounding test, and appear as small dull 
yellow rounded s]3ots. They are not distinctly divided into regions. 
The Test is firm and massive, and is almost quite opacpie. The small cells are ex- 
ceedingly numerous ; most of them are more or less rounded in form. 
The Mantle is moderately strong, and most of the muscle bands run longitudinally. 
The Branchial Sac is small and opaque. The stigmata are small rounded aper- 
tures. 
Locality. — Simon’s Bay; depth, 10 to 20 fathoms. 
The specimen obtained at Simon’s Bay, from which the preceding description has 
been taken, is very closely allied to Atopogaster elongata, and it is probably best to 
regard it as a variety of that species. The shape although still elongated from the base 
upwards is more irregular, the surface being strongly hidged and grooved (PL XXIV. fig. 9)', 
