172 
ZOOPHYTA ASTEROIDA. 
pagated are the peculiar products of the lining of the abdominal 
cavity. The ova sometimes originate in its lamellae, sometimes 
from the interspaces, and in other cases from the walls of the 
permeating canals. In Pennatula we first detect them between 
the membranes of the polypiferous pinnae ; in Alcyonium in the 
cartilaginous canals which are traced through the polype-mass, 
or in the abdominal sac sprouting from the plaits ; and in Gorgo- 
nia, Cavolini informs us, they germinate in eight distinct 44 ova- 
ria at the base of each polypus.” They first appear like a 
minute smooth wart which gradually rises up from the surface, 
enlarging itself at the same time, and when a certain size has 
been attained, the wart becomes constricted at its base, then 
shortly pedicelled, and at last it separates a free egg by the absorp- 
tion of this retaining neck or umbilical cord. (Plate xxvi. Fig. 6.) 
The eggs now at liberty to move, gradually approach the base 
of the stomach, which, as already mentioned, is perforated with 
an opening that can be made wider or closed by means of its 
sphincter muscle. After several approaches and as many repul- 
sions, the aperture at length allows the egg to pass through into 
the stomach, whence it is ejected through the mouth into the 
open sea. Professors Grant and Milne-Edwards have witnessed 
this process in the Alcyonia, and the former also in the Penna- 
tula and Virgularia ; but in the Gorgonia, according to Cavo- 
lini, the ova pass upwards 44 through eight small oviducts,” and 
are discharged, by as many apertures, 44 between the bases of the 
eight tentacula.” # 
The structure of the ova has been well described by Cavolini, 
and more especially by Professor Grant. Before their detach- 
ment they seem, in general, to be white, but when mature they 
are almost always vividly coloured, globular, and apparently 
smooth, but clothed, as the microscope shews, with short cilise, 
which by their vibration cause them to move to and fro as if 
they were actuated by volition. They are membranous capsules 
filled with a gelatinous matter composed of very minute transpa- 
rent globules similar to those which compose almost all the soft 
parts of animals, or like the sporules of the lower cryptogamic 
plants. The investing capsule is soft and irritable, for during 
their motions the ova are seen frequently to contract themselves 
* Edin. New Phil. Journ* i. 152. 
