9 6 



ECHINOIDEA. I. 



Perrier 1 ) and Stewart 2 ) have given informations of the spicules in several genera and species, 

 and especially Stewart thinks that they will be found to afford most valuable and interesting addi- 

 tional points of generic and specific distinction . I must think it very improbable that good specific 

 characters should be found in the form of the spicules; as far as my examinations reach they are very 

 similar in all the species belonging to the same genus. On the other hand I quite agree with Ste- 

 wart that the spicules yield valuable generic characters, and even excellent family characters. — The 

 most common type is the simple, c-shaped, bihamate form ; it is found in Echinus and Echinometra 

 and the genera more nearly allied to these. In Strongylocentrotus drebachiensis and some other Stron- 

 gylocentrotus-STpea.es the form is the same, only that here the spicules are a little branched in the 

 ends (PL XX. Fig. 12). A very peculiar form of spicules is found in Toxopneustes, Pseudoboletia, 

 Spheerechznus, and upon the whole in the forms with deep mouth-slits. They are dumb-bell-shaped, 

 as two small balls connected by a short bar (PL XXI. Fig. 28 etc.). In Sphcerechinus they resemble 

 more the common bihamate spicules, but they are not at all pointed at the ends. Also a few typical 

 bihamate spicules maybe found among the others; this is also the case in Strongylocentrotus. Some- 

 times all possible stages of development of these spicules may be found, from a little ball to the form 

 of the dumb-bell, and farther to the bihamate form (PL XXI. Fig. 31). That these forms are really 

 developmental stages can, I think, scarcely be doubted. It is evident that a considerable rearrange- 

 ment of the mass of lime must take place; but a similar resorption and new deposition of the lime is 

 already known from Theels examinations of the resorption of the larval skeleton in the Echinoderms3). 

 The form of spicules mentioned here is an excellent character of the family Toxopneustidm (see below). 

 Another peculiar form of spicules is found in Parasalenia and Anthocidaris\ they are arcuate, with 

 1 — 2 small projections in the middle (PL XXI. Figs. 30, 32). Stewart calls this form of spicules ■ bia- 

 cerate . Also common bihamate spicules are found together with these, but in small numbers. A 

 quite unique form of spicules is found in Slomopneustes; they are of two kinds: smaller, irregular 

 fenestrated plates, and large, thorny, perforated tubes that may be a little branched (Stewart. Op. cit. 

 PL L. Fig. 1). 



The spicules are especially found in the tube feet, but also in the skin round the pedicellariae 

 (especially the globiferous ones), both on the stalk, the neck, and the head, and round the base of the 

 spines they occur frequently. In the gills and the buccal membrane bihamate spicules are often found 

 together with the more or less irregular fenestrated plates that are commonly found here. Also the 

 inner organs are often richly provided with spicules that may be of a very irregular form, as has 

 been shown by Stewart with regard to Echinometra. This, however, is of no practical importance 

 in the classification where regard must chiefly be paid to the regular spicules of constant form in 

 tube feet and pedicellariae. 



With regard to the pedicellariae we have some good informations, especially in the works by 

 Perrier and Agassiz. From these informations it is evident that an abundance of peculiar struc- 

 tures may be found here which are, no doubt, of great systematic importance. Thus Perrier has 



') Recherches sur les Pedicellaires et les Ambulacres des Asteries et des Oursins. Ann. Sc. nat. 5. Serie. Zool. 

 T. XII— XIII. 1869—70. 



2 ) On the Spicula of the Regular Echinoidea. Trans. Linn. Soc. XXV. 1S65. 



3) Notes on the formation and absorption of the skeleton in Echinoderms. Ofvers. Kgl. Vet Akad. Forh. 1S94. 



