AGA Proceedings of Philosophical Societies. [JuNE, 
their hermaphroditism is complete, so that they suffice themselves 
like the oysters, and many other bivalves. 
M. Cuvier has likewise given a memoir on the ascidia, a kind of 
moluscea enveloped, not in a shell, but in a cartilaginous crust, fixed 
to the rocks, and provided with two openings, one of which re- 
ceives and rejects the water necessary for respiration, and the other 
affords an outlet to the ova and excrements. A great cavity covered 
with a fine vascular net, which comes in place of the branchie, 
receiyes this water, and with it the corpuscula with which the 
animal is nourished, At its bottom is the mouth, which leads to a 
sort of gizzard. These animals have a heart, liver, and nervous ‘ 
system, pretty similar to that of other molusca. But the relative 
disposition of these parts, as well as the form and surface of the 
external envelope, varies much, according to the species. 
This anatomy of the ascidia was so much more to the purpose, 
because it served to elucidate observations of a much more novel 
and important nature, which were made almost at the same time on 
animals of a similar nature, by M. Savigny, Member of the Insti- 
tute of Egypt. 
No compound animals are yet known except those in the order of 
polypi. All the corals, madrepores, sea pens, and a great many 
alcyonia, appear merely aggregations of different polypi united in 
an intimate manner, and whose nourishment takes place in common, 
so that what one eats is of use to all, and they all seem animated by 
acommon will. This last circumstance is certain at least with sea 
pens, which transport themselves from one place to another by the 
combined and regular rowing of thousands of little polypi which 
proceed from all the feathers. The structure of these polypi is suffi- 
ciently simple for the imagination to conceive this kind of associa~ 
tion, which we may in some measure compare to the different 
branches of the same tree. 
But M. Savigny has discovered compound animals of another 
kind, and whose individual organization is much more complicated. 
They bear a singular resemblance to those molusca called ascidiz, 
which themselves have some analogy with the animals of bivalve 
shells. We find in them equally a bronchial sack, which the ali- 
ments are obliged to traverse to arrive at the mouth; a muscular 
stomach ; an intestine, of which the rectum mounts towards the 
side of the mouth, and forms there a second orifice; a nervous 
ganglion placed between the bronchial orifice and that of the anus ; 
an ovarium, and an oviduct. In fact they are real ascidize united 
in masses by a common flesh, and partaking, in consequence, of a 
common life. ‘This sort of animal aggregation had been hitherto 
confounded with the alcyoniz. They are numerous; and M. 
Savigny, who has described and represented them with details to 
which their singularity entitled them, has observed a sufficient 
number of forms in them to constitute eight genera. 
Among these compound animals some form fixed masses more or 
less irregular, as is the case with many alcyoniz ; others are ranged 
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