44 



C. Functions of the Pcdicellaries. 



With regard to the nature and destination of these remarkable small organs, which, 

 as is well known, are only peculiar to the proper star-fishes and to the Echinidse, and which 

 in the Brisinga exhibit a remarkably complicated structure, appearing also in greater number 

 than in any other known Echinoderm, many and various conjectures have been set forth, 

 without apparently elucidating their homology or their functions. Without flattering myself 

 that I can solve the difficult problem in a perfectly satisfactory manner, I think that I ought 

 here to set forth my views as to the latter point. The homology of the pedicellaries will 

 be noticed more particularly in a subsequent section. 



From the structure of the pedicellaries it may certainly be inferred that they are 

 destined to seize and hold fast the objects which come in contact with them. Whether 

 however the intention is to protect the tender and sensitive exterior cuticle, or to retain 

 such particles as may serve the animal for food, is a question about which the opinions 

 of the authors do not yet quite agree. In the Echinidte it has certainly been ascertained, 

 by direct observations on the living animal, that the pedicellaries play an important part in 

 removing the excrements expelled from the anal aperture, which else might easily become 

 entangled among the numerous spines and thereby hinder the free play of the water-feet, 

 and also pollute the fine layer of skin between the spines. For this purpose, only the 

 pedicellaries situated in the upper half of the shell are required. But pedicellaries in just 

 as great abundance are found also on the lower side of the shell, close up to the nearest 

 environs of the mouth, where they even appear in quite unusual numbers. These pedicel- 

 laries must certainly have a widely different destination in the economy of the animal. It is 

 here in my opinion most natural to think of a retention of such particles as should serve 

 for food, and which probably would be brought within reach of the mouth in a manner 

 similar to that in which the excrements on the other side are conveyed away down the 

 sides of the shell. 



A similar difference in the pedicellaries' functions may in my opinion also be pre- 

 sumed to exist in the Brisinga. The pedicellaries situated on the dorsal side of tbe body 

 and especially on the numerous soft transverse ridges of the arms, are probably chiefly in- 

 tended for the removal from the dorsal surface of various extraneous matter (particles of 

 mud &c) which might come in contact with them; thereby protecting the interjacent naked 

 cuticle. But on the whole, we must certainly presume that those pedicellaries have a different 

 destination, which are found in masses on the cuticular sheaths of the spines, attached to 

 the skeleton of the arms and of the disc, especially those at the extreme ends of the same. 



We might indeed imagine, as regards the innermost furrow-spines, that the pedicel- 

 laries attached to them were intended to prevent extraueous particles from penetrating and 

 irritating the thin sensitive skin which covers the ambulacral furrows; and according to 



