ACTINOZOA. 135 



'acontia,' are occasionally met with. Both cras- 

 peda and acontia are richly furnished with thread- 

 cells, for the emission of which special apertures 

 along- the wall of the somatic cavity have, in some 

 species, been observed. Mr. Grosse, who gives the 

 name of ^cinclides' to these apertures, describes 

 them as varying considerably in size and opening 

 directly into the somatic chambers. " Each is an 

 oval depression, with a transverse slit across the 

 middle." The sides of the cinclis can be opened 

 or closed at the animal's pleasure, yet, when sepa- 

 rated to their utmost extent, the front of the 

 orifice is seen to be protected by a very thin 

 superficial film. 



In the common Sea-anemone the margin of the 

 disc is furnished with a series of whice or bright 

 blue specks, which some writers describe as a 

 rudimentary apparatus of vision. The structure 

 of these organs is not yet fully understood. Like 

 the body-warts, mentioned elsewhere, they are 

 probably to be regarded as sac-shaped prolonga- 

 tions of the outer layer. 



Grood evidence has not yet been brought forward 

 of the existence of a nervous system in Actinia, 

 A muscular apparatus is, however, well developed, 

 and has been described in detail by M. Hollard. 

 In the inner layer of the body-wall are two sets 

 of flattened muscular fibres ; a superficial circular, 

 and a deeper longitudinal. Each mesentery has 

 four muscles, two for each of its faces. The 

 stomach wall is also provided with its own mus- 

 cular fibres, these being so arranged in the vicinity 

 of the inferior aperture as to permit the latter to 

 be closed at pleasure. The existence of this 

 sphincter is denied by some observers. A similar 



K 4 



