Sub-kingdom, MOLLUSCA. 
Class, CILIOPODA, f = Polyzoa = Hryozoa ). 
I 
Character. — Acephalous Mollusca, consistiny of a simple mantle-sac, only open 
on the anterior side, enclosing all the other organs, which are entirely or mostly 
retractile loithin the sac,its margin being more or less thickened, or sometimes produced 
into arms, hut in all cases prodded idth a row of finely ciliated tentacles; within 
these the mouth is situated, on the dorsal side of lohich terminates the anus. A 
single ganglion lies between the mouth and the anus. The animals are hermaphrodites, 
but the propagation also consists in a repeating gemmation, on account of which they 
form more or less extensive, partially free-growing or entirely attached colonies, 
composed of variously shaped, horny, or chitinous or calcareous, cells or kibes lohich 
are secreted by the animals ; they are all aquatic. 
This diaractcristic is a Tcry general one, but it is common to all known Cilio- 
pods, and suffices to distiuguisb them readily from all the other classes of Mollusca. 
In the way of an explanation I shall add a few details regarding their organisation ; 
these must necessarily he brief and only refer to the principal organs. It is, at the 
present stage of our knowledge, extremely difficult to supply a satisfactory general 
account of the class, because the only good anatomical descriptions Ave possess 
chiefly refer to the fresh Avater forms, as knoAvn from the able researclies of Dumor- 
tier and A'an Beneden, Allman, Ilyatt, and others, Avhile of the marine Ciliopoda 
a comparath'ely A'ery small nunrber of animals has been examined by A'arious authors. 
As it is, however, the olAject of the folloAving pages to give an idea of the organi- ) 
sation of the latter group, I Avill confine my remarks chiefly to those characters 
Avhich are, from more or less detailed obserA'ation, knoAvn to be common to both. 
ddie body rcinesents a simple, either cylindrical or bottle-shaped sac, AA'hich is 
open and free on one side, and on the opposite connected by a thin cord Avith the pre- 
Auous cell, from Avhicli the former sprang up by gemmation. The sac or cell 
consists of two structmns, the so-called cctocyst and the endocyst, each of 
Avhich is again composed of scA'cral layers of cells and muscular fibres, the 
endocyst haA'ing, according to Hyatt, fiA'e such different layers. The ectocyst secretes 
either horny or chitinous particles in the fleshy soft mass, or a regular continuous 
membrane of those substances, or else a calcareous crust, Avhich defines the external 
shape of eacli cell, communicating by one or scA'eral canals with the neighbouring 
cells. The calcareous ectocyst is, howcA'cr, not secreted in distinct superposing 
layers, but in single fibres, which are placed vertically to the body, and are traA'crsed , 
by numerous canals, terminating on the outer surface as so many larger and . 
smaller pores. i 
( 35 ) 
