38 ALLMAN, ON POLYZOA. 
An arrangement which appears to us to be very natural and 
convenient. The definitions, however, of the marine gymno- 
leematous sub-orders do not include certain characters perhaps 
fully as important as those here given. The Cyclostomata are 
distinguished from the Cheilostomata, as much by the ter- 
minal position of the orifice of the cell, as by its bemg unfur- 
nished with a moveable lip or operculum; and from the 
Ctenostomata, not more by the absence of the fringed or 
setose margin to the orifice of the cell, than by the cir- 
cumstance that in them the cells arise by gemmation one 
from the other, as do those of the Cheilostomata, whilst in the 
Ctenostomata, or, as perhaps they might move appropriately 
be termed, the Crossostomata, the cells arise each separately 
from a common tubular stem, with whose cavity that of 
the cell communicates. The sub-terminal position of the 
orifice of the cell appears to be an essential characteristic 
of the important and numerous group of the Cheilo- 
stoma. 
The terminology employed by Professor Allman in the 
description of the Polyzoa, differing from that heretofore 
used, which has been very confused and unsatisfactory, 
demands attention, inasmuch as, with perhaps the exception 
of one term, it seems to us highly desirable that it should be 
generally adopted. The retractile portion or zooid, he terms 
“ nolypide ;” to the common dermal system of a colony— 
often erroneously termed ‘ polypary” and “ polypidom”’—he 
apples the term “ coencecium ;” this part consists almost 
universally of two perfectly distinct tunics — the outer 
of which is the “ ectocyst,’ whilst the internal is termed 
“endocyst.” The sort of disc or stage, which surrounds 
the mouth and bears the tentacula, is called the ‘“ lopho- 
phore,’ whilst the “epistome” is a peculiar valve-like 
organ which arches over the mouth in most of the fresh- 
water genera. The “ perigastric space” is the space included 
between the walls of the endocyst and the alimentary canal. 
The canecium is composed of the little chambers, or “cells,” 
in which the polypides are lodged, whilst that part of the ced/ 
through which they protrude is the “ orifice.” 
With reference to these terms, we would observe, that the 
term polyzoary, or in Latin, polyzoarum, which we have 
elsewhere employed, appears to us to be more likely 
to receive popular acceptation than the more recondite 
word, cenecium. 'The terms “ ectocyst” and “ endocyst,” 
though strictly applicable and highly appropriate nearly 
throughout the Polyzoa, must, when employed in the descrip- 
tion of the Ctenostomata, be somewhat strained when used to 
