on the Natural Group of Tunicata. 531 
rvesèn), and communicating with a fleshy intestine (c? cagxddsc) ; 
so that the intestine of the Tethyon appears contained in this 
reticulated membrane. Although, indeed, the flesh is alike in 
all testaceous animals, this intestine resembles in form that of 
none of them. It is suspended at two places, viz. to the above- 
mentioned membrane, and to the muscle* which proceeds from 
the side; and wherever it adheres to either of these it is narrowest. 
At each point of suspension this intestine tends towards those 
orifices which lead to the outside of the test, and by which it re- 
ceives and discharges its food and water; so that if one of these 
apertures be the animal's mouth, the other must be its anus. One 
of these orificial processes is thickert than the other. Within 
the cavity also of one or other of them there is a certain small 
cohering substance which divides it." 
These preliminary remarks, and particularly this accurate 
though ancient description of an Ascidia, will be sufficient to 
enable any person to pursue the tenour of the following de- 
scriptions: but in order to understand them thoroughly, I need 
scarcely say that a perusal of the admirable memoirs of Cuvier 
and Savigny is indispensable. 
The TuN1cArTA 1, then, are animals which connect the Acrita 
or lowest primary dion of the animal kingdom with the Mo/- 
lusca. From the Mollusca, however, they differ in having an exter- 
nal covering consisting of an envelope distinctly organized and 
provided with two apertures, of which one is branchial, the other 
anal. "They also differ from the Mollusca as well in their mantle 
* Literally it is *to the skin from the side;" and in fact the suspending muscle is 
exceedingly like a piece of the tunic. 
* This is the branchial orifice; and I suspect that the small cohering or continuous 
substance which Aristotle alludes to immediately afterwards, is the valvule of the anal 
orifice. À 
+ According to his usual practice of changing names,—a practice which interferes 
so much with his well-merited reputation,—M. de Blainville calls this group Hetero- 
branchiata, a name without one single quality to recommend it. 
VOL. XIV. 3 Z forming 
