DIVISIONS OF THE HYDROZOA. be. 
through the above-mentioned aperture to the cavity of the coeno- 
sarc, which, by the combined éxertions of the whole assemblage 
of polypites, thus becomes filled with a granular nutritive liquid. 
This coenosarcal fluid is in constant movement, circulating 
through all parts of the colony, and thus maintaining its vitality 
—the cause of the movement being probably due, in part, at any 
rate, to the existence of vibrating cilia. 
The process of reproduction varies somewhat in different 
members of the order. In all alike, however, the ordinary 
polypites are incapable of producing the essential elements of 
reproduction, and for this purpose special generative buds have 
to be developed. In the typical Sertularians the reproductive 
buds are developed at certain seasons in great numbers, and 
they constitute what used to be called 
the “ovarian vesicles” or “capsules” 
(fig. 21). These reproductive buds are 
enclosed in horny cups or receptacles, 
often of a very beautiful shape, and 
much larger in size than the ordinary 
hydrothece (fig. 20, a, d) Each bud 
may be compared to a polypite destitute 
of a mouth and tentacles, being composed 
of a protuberance of the ectoderm and 
endoderm, containing a prolongation from 
the general cavity of the ccenosarc. 
The essential elements of reproduction 
are developed between the ectoderm and 
endoderm of the bud, and the resulting _ 
embryo is finally liberated asa little oval * ee Se eena nee. 
body covered with cilia, with which it  ofercudata, Linn. (After 
swims freely about, until it meets with gq -Hincks.) Greatly en- 
3 ; i : larged. 
suitable locality, when it fixes itself, loses ; 
its cilia, and by budding soon develops another colony. As 
a general rule, each capsule in the Sertudarida contains a num- 
ber of the reproductive buds, which are all borne upon a centra 
axis which runs up the middle of the capsule, and is derived 
from the coenosarc. 
In one division of this group—often described as a separate 
order, under the name of Campanularida—some points of dif- 
ference are observable. In the typical Sertularians the little 
cups or hydrothece for the polypites are placed on the sides of 
the branches, and they are not stalked (fig. 20, 4), whilst the 
