172 ZOOPHYTA ASTEROIDA. 



pagated are the peculiar products of the Hning 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 " 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 lastit separates afree egg by the absorp- 

 tion ofthis retaining neckor 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 " through eight small oviducts," and 

 are discharged, by as many apertures, " between the bases of the 

 e\a\\i 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 ciliae, 

 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. Now I'hil. Jouiii. i. 15-2. 



