THE ANATOMY OF CATJDINA COBIACEA. 459" 



anterior being on one side presumably as yet undeveloped. It 

 will be seen tbat the largest tentacle is placed most posteriorly 

 in the middle of the group. It is strictly radial in position and 

 evidently corresponds to the terminal tentacle of Grerould, being 

 homologous, as that author has pointed out, with tbe terminal 

 tentacle of Asteroids. It will also be seen that there are no 

 suctorial disks and no end-plates, but that the larger tentacles, 

 in this respect unlike those o£ C. arenata, contain irregularly 

 branched spicules scattered in their walls. In the specimea from 

 which fig. 2 is taken no trace was visible of anal teeth, the five 

 projections which are supposed to represent them having com- 

 pletely disappeared, nor have I found them in any but the very 

 youngest individuals. The specimens in which Theel discovered 

 them appear to have been mere fragments of tails ; and we must 

 assume either that these also belonged to extremely young 

 individuals or that be was referring to the five largest anal 

 tentacles, uuless it be that the teeth persist in some individuals 

 and not in others. 



Having thus described the external appearance of the organs 

 surrounding the anus, we may pass oa to investigate their 

 relations to the internal structures. This may be done by means 

 of a series of transverse sections of the so-called tail of one of 

 the youngest specimens. 



The general arrangement of the parts concerned is shown in 

 PL 29. fig. 3, which represents a transverso section taken at 

 some little distance in front of the anus (the bOth section from 

 the posterior extremity). 



It will be seen that the integument is here very thick, and that 

 the cloaca is attached to the body-wall by very numerous radi- 

 ating bands of muscle. These deserve a brief notice. Each 

 consists of a hollow cylinder of fibres running lengthwise side 

 by side, and covered externally by a thin layer of epithelium 

 containing many conspicuous, darkly-staining nuclei. 



Grerould describes in Gaudina arenata certain muscle-cylinders 

 which run outwards through the connective-tissue layer of the 

 integument and terminate immediately beneath the epithelium. 

 He points out that the striking resemblance of these muscular 

 tubules to the vessels which connect the ambulacra with the 

 radial canal, led Semper to the erroneous conclusion that they 

 are actually in connection with the canal. Grerould himself 



