184 ZOOLOGY 
includes an immense number of species, and has been divided 
into two subdivisions: (i.) the PHYLACTOLAEMATA, which 
inhabit fresh water; and (1i.) the GYMNOLAEMATA, which are 
almost invariably marine. 
The Phylactolaemata are further distinguished from the 
Gymunolaemata by the presence of an epistome and the shape 
of their lophophore, which is that of a horse-shoe, and by the 
formation of statoblasts. The structure of a member of this 
subdivision has been illustrated by the description of Pluwmatella ; 
in this genus the body-cavities of the various polypides are in 
communication, though some of the polypides are partially 
separated by an imperfect septum. In Lophopus and Cristatella 
the coelom in each polypide is in free and open communication 
with that of all the others. The last-mentioned genus forms 
colonies, which may attain the length of over two inches. The | 
colony is oval in outline, and the polypides project from its 
upper convex surface; the lower surface is flat, and on this the 
whole colony creeps slowly along on submerged stems or stones. 
This mode of progression of the colony is one of the very few 
instances of any co-ordination of function which exists between 
the various individuals which compose a Polyzoan colony. 
The Phylactolaemata are all hermaphrodite. 
The Gymnolaemata have a circular lophophore, and are 
devoid of an epistome. With the exception of a few genera, 
they are marine. In Paludicella the funicular tissue of the 
various individuals communicates by means of certain perfor- 
ations known as rosette plates, but in the marine forms the 
zoeecia are more independent. The ectocyst may be calcareous, 
horny, or gelatinous, and the various zooecia may be aggregated 
together in an almost infinite variety of ways. From time to 
time the polypide dies down, the tentacular crown and aliment- 
ary canal degenerating and forming what is known as the 
“brown body,” which is coloured by the concretions which 
have accumulated within the wall of the stomach. This 
brown body lies in the zooecium until the endocyst produces 
a bud, and then it may become included in the alimentary canal 
of the bud or young polypide; here the nutritive matter which 
it may contain is doubtless absorbed, and the undigestible 
matter passes out of the intestine of the young polypide. 
