1 84 ZOOLOGY 



includes an immense number of species, and has been divided 

 into two subdivisions : (i.) the Phylactolaemata, which 

 inhabit fresh water ; and (ii.) the Gymnolaemata, which are 

 almost invariably marine. 



The Phylactolaemata are further distinguished from the 

 Gymnolaemata 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 Plumatella ; 

 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 Loplwpus and Gristatella 

 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, surf ace 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 Faludicella the funicular tissue of the 

 various individuals communicates by means of certain perfor- 

 ations known as rosette plates, but in the marine forms the 

 zooecia 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. Prom 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. 



