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ginal spines there are in the Brisinga only the dorsal; ventral marginal plates being, as 

 previously noticed, entirely wanting. The dorsal marginal spines have however precisely the 

 same arrangement along the sides of the arms as in other star-fishes. The furrow-spines 

 have likewise, apart from their number, on the whole the same arrangement as in other 

 star-fishes, those on each adambulacral plate forming a (certainly not quite regular) trans- 

 verse row, and those on the innermost contiguous adambulacral plates assuming also in the 

 Brisinga a peculiar form and direction as real oral spines. 



d. Homology of the pedicellaries. 



The pedicellaries in the Brisinga are of a very similar structure to those of several 

 other star-fishes, for instance Asterias, Pedicellaster. On the other hand they differ by their 

 comparatively insignificant size, their enormous number and their ditl'erent arrangement. 

 While those of the other star-fishes are more dispersed on the skin, or at most group 

 themselves in some quantity around the base of the larger spines (Asterias) those of the 

 Brisinga are present in enormous numbers on the cuticular sheaths of the spines them- 

 selves; and those which are attached immediately on the dorsal skin of the arms are col- 

 lected, likewise in enormous numbers, into plainly defined transverse stripes, which can 

 even assume the form of semicylindrical transverse ridges (Br. coronata). As regards the 

 general homology of the pedicellaries, their position on the cuticular sheaths of the spines 

 shews clearly enough, that they cannot be, as Agassiz* has tried to demonstrate, originally 

 homologous with the spines. These latter are developed from the interior cuticular layer 

 (coriuni) while the pedicellaries are, as the development also shews, (see above p. 64) exclu- 

 sively an epidermis-formation. It may indeed in a certain sense be said that the so-called 

 pedicellaries of the Echinidje are homologous with the spines. But what we call pedicel- 

 laries in the Echinidte are, it must be remembered, essentially dift'erent from what we call 

 by that name in the star-fish. A pedicellary of the former is properly a compound organ 

 including a spine, beneath the proper pedicellary, (the so-called stem of the pedicellary); 

 such a pedicellary is in other words a real spine, on the cuticular sheath of which there 

 is only developed one single terminal pedicellary; and it cannot therefore be compared 

 with a single pedicellary of a star-fish, which never has any such actual stem as in the 

 Echinidse. 



e. Homology of the interior organs. 



With regard to the other organic systems in the Brisinga: the water-system, with 

 the exterior parts belonging thereto, (the water-feet, the madreporic body); the nervous 

 system with its terminal apparatus of sensation; the digestive system; the blood-system ; the 



* Revision of the Echini, Part IV, pg. 668. 



12* 



