96 



ECHINOIDEA. I. 



Perrier') and Stewart^) have given informations of the spicnles in several genera and species, 

 and especially Stewart thinks that they will be fonnd 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 veri- 

 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 e\-en 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 Strongylocentrotiis drobachiensis and some other Strou- 

 gylocenirotus-s^&cie^s the form is the same, only that here the spicules are a little branched in the 

 ends (PI. XX. Fig. 12). A very peculiar form of spicules is found in Toxopiicustrs^ Psnidobolefia, 

 SphcBrechwus^ and npon the whole in the forms with deep mouth-slits. They are dumb-bell-shaped, 

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

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

 bihamate .spicules may be 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 (PI. XXI. Fig. 31). That these forms are really 

 developmental stages can, I think, scarcely be doubted. It is e\ident 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 P^chinodermsS). 

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

 Another peculiar form of spicules is found in Pa rcr sal en in and Aiifliocidaris\ the>- are arcuate, with 

 I — 2 small projections in the middle |P1. XXI. F'igs. 30, 32). Stewart calls tliis form of spicnles bia- 

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

 quite imique form of spicules is found in Stomopncustcs; the)- are of two kinds: smaller, irregular 

 fenestrated plates, and large, thorny, perforated tubes that ma\- be a little branched (Stewart. (_)p. cit. 

 PI. L. Fig. I). 



The spicules are especial!}' found in the tube feet, but also in the skin round the i:)edicellaria; 

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

 spines the\' occur frequently In the gills and the buccal membrane bihamate s]:)icules are often found 

 together with tlie 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 inqiortance 

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

 tube feet and pedicellarise. 



With regard to the pedicellarise 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. Tlius Perrier has 



■) Recherches sur le.s Pediccllaires et Ics Aiiil)ulacre.s dcs Asterics et des Ounsins. Aim. Sc. uat. 5. Serie. Zool. 

 T. XII-XIII. 1869—70. 



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



3) Notes on the formation anil ahsorjnion of the .skeleton in Echinoderms. Ofvers. Kgl. Vet .Vkad. Forh. 1S94. 



