on the Natural Group of Tunicata. 545 
mach in a spiral form may so be considered. The stomach is 
internally simple, with very slight transverse striæ. 
The heart is situated horizontally between the lower part of 
the tunic and the stomach. It is large, ovoidal, and appears to 
be composed of several lobes, and is indeed of a structure diffe- 
rent from that of such Ascidide as are known. There are four 
vertical openings to it, which are capable of being widely dis- 
tended. 
The dorsal sulcus is remarkably distinct, and proceeds from 
the immediate vicinity of the heart, or rather along the back of 
it, to that of the branchial orifice. It may be seen through the 
external envelope of the body, when this is viewed on the left 
side, and forms an arch enclosing a lesser and more pointed 
arch, which last appears to be nothing else than one of the folds 
of the branchial pouch. At the point where this last arch touches 
the dorsal sulcus there is in our specimen an orifice opening ex- 
ternally, and apparently communicating by a tube with a beau- 
tifully diaphanous longitudinal pouch, which contains nothing 
but two blackish nodules, one of which is longer than the other. 
The imperfection of the only specimen in my power to examine 
has prevented me from accurately ascertaining the nature and 
use of this organization, which appears to have nothing similar 
to it in any of the other Tunicata hitherto observed. 
Tue third animal whose structure I have to explain belongs to 
the natural 
Genus ASCIDIA Linn. Cynthia Sav. 
EXTERNAL CHARACTER. Body sessile, with a coriaceous test, 
having both orifices quadrifid, or at least having the 
anal orifice very rarely transversely cleft. : 
ANA- 
