upon the Structure and Oeconomy of Tenia. - 253 
The central ftruéture of veffels placed in each joint feems calcu- 
fated to abforb the fluid from the alimentary canal, for the imme- 
diate purpofe of fuftaining and repairing the parts of the body in 
their vicinity, which is probably done by depofition, but there 
ftill remains a great deal of cellular fubftance into which no veffels 
enter*, Such parts of the bodies of thefe animals are poflibly 
nourifhed by tranfudation of the alimentary fluid into their cells, 
or it may be effected by the capillary attraction of their fibres. 
lt appears that there are animals totally deftitute of vafcularity, 
as {ome fpecies of Hydatids, Polypi, &c. in which tranfudation of 
fit matter, or capillary attraction by their fibres, feems to be the 
only fource of nourifhment. As Tæmæ have no excretory ducts, 
the decayed parts of their bodies are, moft likely, diffolved into a 
fluid which tranfudes through the fkin like perfpiration, and with. 
their purpofes. I have never feen any thing refembling brain or 
nerves in the Tæwæ; but as they are highly fenfible to ftimuli, it is 
moft reafonable to conclude, that they have a confiderable portion 
of nervous matter in the compofition of their bodies, that is, of fuch 
matter as is fufceptible of ftimuli. Indeed we can hardly conceive 
how any animal can exift without fuch matter in its compofi- 
* The Tenia feems to be one of the moft fimple vafcular animals in nature, and its 
central tructures of veflels appear to be more like refervoirs for the nutritious fluid, 
than circulating veffels,. for the contained fluid can only be pufhed out of one canal. 
into another, and even then it will not have vifited all the parts of the animals body. 
Probably this kind of conftruétion enables thefe animals to live for a confiderable time 
without food, which their fituation and imperfe& form may render neceflary. As this 
animal has no anus, it would appear that the whole of its alimentary fluid is fit for 
nourifhment, and that no part of it is excrementitious. 
8. te na 
