190''] Jennings. — Behavior of the Starfish. 65 



animals, thoniih it is directed mainly toward conservino; the 

 welfare of the stai-fish as a whole, rather than toward the pres- 

 ervation of the individual pedieellaria as would doubtless be the 

 case if they were independent. Bnt behavior with the mere 

 object of self-preservation, comparable to the fleeing away of an 

 entire animal, is found in pedicellariae under certain desperate 

 conditions. 



The behavior of the pedicellariae of the sea-urchin has been 

 studied with great thoroughness by von Uexkull (1899), and 

 his observations will be of interest for comparison with what 

 we find in the starfish. In his paper von Uexkiill gives an 

 extended history of the development of our knowledge of the 

 pedicellariae in both the sea urchins and the starfish, and of the 

 various theories that have been held as to their nature and func- 

 tion ; it will therefore be unnecessary to give such an account 

 here. No detailed study of the physiology of the pedicellariae 

 of the starfish has been published,, though, as we have seen, 

 Cuenot describes briefly their action in protecting the gills from 

 small M'orms. 



Kinds of PedieeUariae. — The starfish under consideration 

 (Asterias forreri) has two kinds of pedicellariae, differing much 

 from each other, together with a third kind that is in some 

 respects intermediate between the two others. By far the most 

 numerous are the pedicellariae already described (fig. 1). which 

 are grouped in the rosettes or rings surrounding the spines. 

 These have the typical structure of the common starfish pedi- 

 cellariae. The two jaws form a cross, like a pair of pliers, with 

 a third piece between them, on which they move as on a pivot. 



Among these are scattered a few enormous pedicellariae. 

 nearly as large as the spines of the starfish. These are not 

 grouped, but usually stand solitary, rising from the surface of 

 the body among the spines: not infrequently two or three are 

 placed close together. They are formed on the well-known type 

 of a basal piece, on which rest the two jaws, not crossing, but 

 opposed throughout their length; they may, therefore, be com- 

 pared in structure to a pair of sheep shears. The number 

 and distribution of these large pedicellariae vary in different 

 individuals. Some have hardly one; others bear a dozen or 



