148 ANTIIOZOA ASTEROIDA. 



as many apertures, " between the bases of the eight tenta- 

 cula,"* we may safely infer that there is an error in his obser- 

 vation, — which, moreover, is at variance with Mr. Couch's 

 experience. ■[■ 



The structure of the ova has been well described by Cavo- 

 lini, and more especially by Professor Grant. Before their 

 detachment they seem, in general, to be white : when ma- 

 ture they are almost always vividly coloured, globular, and 

 apparently smooth, but clothed, as the microscope shews, with 

 short cilife, which, by their vibration, cause them to move to 

 and fro as if they were actuated by volition. They are mem- 

 branous capsules filled with a gelatinous matter comj^osed of 

 very minute transparent globules similar to those which com- 

 pose 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 and alter their form. 

 " When placed under the microscope," says Professor Grant,| 

 " and viewed by transmitted light, they appeared as opaque 

 spheres surrounded with a thin transparent margin, which in- 

 creased in thickness when the ova began to grow, and such of 

 the ova as lay in contact united and grew as one ovum. A 

 rapid current in the water immediately around each ovum, 

 drawing along with it all loose particles and floating animal- 

 cules, was distinctly seen flowing with an equal velocity as in 

 other ciliated ova, and a zone of very minute vibrating cilioe 

 was perceptible, surrounding the transparent margin of all the 

 ova. The progressive motion of the ova, always in a direction 

 contrary to that of the current created by their cilise, was very 

 obvious, though less rapid than in any other zoophyte in which 

 I have observed the same remarkable phenomenon. The spe- 

 cimen suspended in a glass jar filled with pure sea-water I 

 now brought so close to the transparent side of the vessel, that 

 I could examine through it, with the assistance of a powerful 

 lens, and without disturbing the animal, the motions and pro- 



" Edin. New Phil. Joum. i. 152. 



t Com. Faun. iii. p. 54. 



J Dr. Grant's observations, quoted in the text, were made on Alcyonium digi- 

 tatum ; but the generalities may be safely applied to the other families, agreeing as 

 they do with the observations of Cavolini on Gorgonia. 



