368 DR. ALLMAN ON THE ANATOMY AND PHYSIOLOGY OF CORDYLOPHORA. 
This word is used ambiguously by writers, being often employed to designate the 
entire composite fabric, the aggregate result of gemmation; while at other times it 
is intended to indicate each of those peculiar organisms which, almost always 
1 furnished with a mouth and tentacula, are developed upon various points of a common 
living basis, and are eminently characteristic of zoophy tic form. In the following 
paper I shall use the term polype strictly in the latter signification ; and for t e 
entire mass, whether consisting of a single polype, as in Hydra, or of many united 
into a more or less definite assemblage, it will be sufficiently convenient to employ 
merely the term zoophyte^. 
Besides the more definite limits within which it is thus necessary to confine the 
term polype, the requirements of precise description demand the use of a few 
additional terms. To the common living basis by which the several polypes in a 
composite zoophyte are connected with one another, I propose to give the name of 
coenosarcf, and every composite zoophyte will thus consist of a variable number of 
polypes, developing themselves from certain more or less definite points of a common 
cffinosarc. The term polypary has been used with just as little precision as polype, 
being sometimes employed to express this common connecting basis, and at other 
times being applied exclusively to the solid protective structures, whether fomiing 
for the zoophyte an external covering or constituting an internal axis ; the ambiguitv 
which thus results will be got rid of by using the word ccenosarc as here defined, 
.and restricting the term polypary to the solid protective structures of the zoophyte. 
All the hydroid zoophytes can be proved to consist essentially of two distinct mem- 
branes ; to the external of these membranes I shall give the name of ectoderm%, and 
to the internal that of endoderm^. 
ORGANS FOR THE PRESERVATION OF THE INDIVIDUAL. 
1. Ectoderm and Polypary. 
(a.) Ectoderm . — The ectoderm (Plates XXV . and XXVI. figs. 3, 4, 9a, a, a) is a well- 
defined membrane ; it is composed of cells, and forms the external layer of the polypes 
andcoenosarc. Multitudes offcac^-ceZ/^aredevelopedinthesubstanceof the ectoderm. 
The thread-cells, when in a quiescent state (fig. 5), present the appearance of minute 
ovate capsules, slightly curved at one end, and with a transparent cylinder occupying 
about two-thirds of the axis. Under the influence of excitement, one extremity of 
* In the following paper the term zoophyte is thus used in its restricted application, by which it is confined to 
the true polype-bearing Radiata, and no more convenient or expressive word can be employed for the purpose. 
If we except the changes which modern research has rendered necessary in removing from the zoophytes of the 
older authors, the Sponges, CoraUines and Polyzoa, this term was used long ago in almost exactly the same 
sense by Pallas, and by Ellis and Solandek, and some of our best living zoologists are now emplo}dng it 
with similar limitations. 
t KOIVOS, 
I eKTOS, Mppa. 
§ eydov, Seppa. 
