96 



ECHINOIDEA. I. 



Perrier") and Stewart^) have given informations of tlie spicnles in several genera and si^ecies, 

 and especially Stewart thinks that < they will be fonnd to afford most valnable and interesting addi- 

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

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

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

 wart that the spicnles yield valnable generic characters, and even excellent family characters. — The 

 most common type is the simple, c-shaped, . bihamate form ; it is fonnd in Echimis and Echinometra 

 and the genera more nearl\- allied to these. In Strongylocoitrotus drubacJiicnsis and some other Sfron- 

 gylocentroius-s])ec\es the form is the same, only that here the spicnles are a little branched in the 

 ends (PI. XX. Fig. 12). A very peculiar form of sjjicules is fonnd in Toxopneustes, Pseiidobolcfia, 

 Sphærechiinis, 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 (PI. XXL Fig. 28 etc). In Sphærcchimis they resemble 

 more the common bihamate spicnles, but they are not at all pointed at the ends. Also a few t^pical 

 bihamate spicnles nia)- be fonnd among the others; this is also the case in Struiigylocciifrofiis. Some- 

 times all possible stages of deveiopment of these spicnles may be fonnd, from a little ball to the form 

 of the dumb-bell, and farther to the bihamate form (PI. 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 dejjosition of the lime is 

 already known from Tliéels examinations of the resorption of the larval skeleton in the Echinodermss). 

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

 Another peculiar form of spicnles is found in Parasalciiia and Anthocidaris; they are arcuate, with 

 I — 2 small projections in the middle (PI. XXI. F'igs. 30, 32). Stewart calls this form of spicnles < bia- 

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

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

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

 PI. L. Fig. i). 



The spicules are especially found in the tube feet, but also in the skin rotmd the pedicellariæ 

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

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

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

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

 been shown by Stewart with regard to Echhiomefra. 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 pedicellariæ. 



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

 Perrier and Agassiz. F'rom these informations it is evident that an abnndance of peculiar struc- 

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



1) Recherches sur les Pedicellaires et les Aiiibulacres des Astéries et des Oursins. Ann. Se. 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. Øfvers. Kgl. Vet Akad. Fcirh. 1S94. 



