90 



stomach and the apparatus of secretion, are in consequence of this limited to a much 

 smaller space than in other star-fishs, (comp. Tab. VI, fig. 36 & 37). 



b. Homology of the skeleton of the skin. 



The integuments in the Brisinga exhibit, as well with regard to consistency as to 

 structure, the most complete resemblance to those of the proper star-fishes; and also the 

 calcareous parts belonging to the skin may be referred to corresponding parts in other star- 

 fishes. It has thus been previously shewn that the calcareous parts imbedded in the dorsal 

 skin of the disc, as well as the very peculiar calcareous ribs in the dorsal skin of the arms, 

 can very naturally be referred to the same category as the so-called calcareous net in the 

 skin of other star-fishes. Also with regard to the so-called marginal plates, likewise be r 

 longing to the skin, we have in the Brisinga something analogous in the small plates, 

 arranged at the basis of the arms or in the angles of the arms, of which the innermost, 

 connected with the wedge-plates, have, in fully developed specimens, entered into the com- 

 position of the oral ring, while the 2 others on each side belong specially to the arms, as 

 evidently developed dorsal marginal plates. Also along the whole of the rest of the arm, 

 there may be noticed, as previously remarked, rudiments of similar dorsal marginal plates, 

 which however in the basal part of the arm go in one with the transversal calcareous ribs, 

 and represent the exterior somewhat enlarged ends of the same. On the other hand, no 

 trace is to be found in the Brisinga of ventral marginal plates ; as also, owing to the com- 

 plete absence of real interbrachial space, there can of course be none of the so-called 

 intermediary ventral plates (interambulacral plates) imbedded in the ventral skin. 



c, Homology of the spines. 



We find in the Brisinga, as in other star-fishes, dorsal spines, lateral or marginal 

 spines, and so-called furrow- spines; the latter are attached immediately to the ambulacral 

 skeleton (to the ambulacral plates) while the others issue from the calcareous parts deve- 

 loped in the skin. 



That the spines in the Brisinga are surrounded by wide cuticular sheaths, seems at 

 first glance to be something quite special and peculiar for this genus. Nevertheless on more 

 minute examination we shall find also in other star-fishes a similar, although slighter and 

 less remarkable cuticular sheath round the spines. Even if this cuticular sheath can not in 

 isolated cases be indicated; it is yet certain that it has originally existed, and has only at 

 a later period been removed. 



As to the arrangement of the spines, this will naturally be regulated by the arrange- 

 ment of the calcareous parts to which they are attached. The different situation of the 

 dorsal spines on the disc and on the aims is quite naturally determined thereby. Of mar- 



