m THE DEVELOPMENT OF COMATULA. 245 



I believe this to be the correct view of the parts in question ; but if we should 

 prefer to regard the single centro-dorsal piece as representing a zone of coalesced 

 basalia, then we must view the five large plates rs parabasalia j for that they are 

 not radialia is manifest from the undoubted relations of the five small interca- 

 lated plates, which must still be considered as radialia, whatever interpretation 

 we give to the centro-dorsal piece. 



The signification of the five large triangular roof-plates still remains to be 

 determined. Now, I have no hesitation in re- Pig. i. 



garding these as iiiter-radialia greatly developed, 

 and, in consequence of the slight development 

 of the radialia, brought into contact with the 

 upper edges of the basalia, to which the}'^ are 

 united, not hy immoveable suture, but by a 

 moveable articulation. In accordance then with 

 these views, the analysis of the body of Coma- 

 tula in the pre-brachial stage, which constitutes 

 the subject of the present paper, will stand as in 

 the annexed woodcut, fig. 1.* 



There is scarcely any more striking feature „, . ^ „ r, ,■ m 



'' "J o Plan of the Fre-Brachial Uomatula. 



in our young Comatula, than the long tentacula- c. Centro-dorsai Piece. 



like appendages or cirri which, in the expanded 2 RadiaiiL 5 



state of the animal, are protruded between the ?. inter-radiaiia, . . 5 



edges of the five roof-plates. A few of those ap- 

 pendages, in an imperfectly extended state, are shown in Duj.-^rdin's and Thomp- 

 son's figures above referred to. Though I have never succeeded in getting a 

 view of their bases, I would regard them as ambulacral feet greatly developed, 

 and otherwise peculiarly modified. Their general resemblance in structure to 

 the " tentacula," which lie in the ambulacral grooves upon the arms, pinnulse, 

 and disc of the more advanced Comatula, is quite in accordance with this view. 



It is more difficult to give a satisfactory account of the long inflexible toothed 

 plates, which, in our larva, lie between the tentacula and the centre ; and I con- 

 fess myself unable to decide as to their real nature, for their structure seems 

 inconsistent with the idea of their being an internal series of modifiedcirri. 



We are now prepared to institute a comparison between our pre-brachial 

 . Comatula and the adult animal. This comparison will show a composition alto- 

 gether different in the two cases. In the adult Comatula, the only distinct pieces 



* Dr Carpenter informs me that lie has detected in an early stage of the larval Comatula, an 

 unsymmetrical " anal'' plate, which he regards as one of a first series of inter-radials (the rest of this 

 series being usually abortive), and which is afterwards lifted by the development of the anal funnel into 

 a much higher position. I have sought in vain for this plate in my specimen, and am of opinion that in 

 the stage to which this specimen belongs, the plate does not exist. It is quite possible, however, that 

 though it has here escaped detection, it may yet be found in specimens better suited for observation. 



VOL. XXIII, PART II. 3 Y 



