NOTES AND MEMOEANDA. 429 



1. The study of the skeleton, whicli has hitherto been neglected, 

 and which is by many naturalists regarded as incapable of furnishing 

 any characters useful in classification, is shown to be " the only 

 means by which the diiferent genera of this class can be rationally 

 distributed in natural groui)s." 



2. The mouth, whatever be its type, is made up of a number of 

 ossicles, of which there are five times as many as there are arms. 



3. The mouth is limited by a number of pieces, of which there are 

 four times as many as there are arms ; these pieces are set in pairs, one 

 of which — amhidacral — forms the extremity of the ambulacra! grooves, 

 while the others — adambulacral pairs — are set between these ; above 

 the adambulacral jiairs, and exactly interambulacral in position, is an 

 azygos piece, to which the name of odontoplwre is given. 



4. This mouth is formed on one of two types : 



(a) In one the ambulacral pairs extend into the interior of the 

 mouth, and limit its contour — amhidacral type. 



(/3) In the other the adambulacral pairs extend into the interior 

 of the mouth — adambulacral type. 



5. These two groups characterize the two sub-classes into which 

 M. Viguier divides the Asteroidea; one, containing the Asteriadw, 

 Heliasteridce, and BrisingidcB, has the ambulacral pairs horizontal, the 

 adambulacral pairs truncated, and an " odontoj)hore " which is not pro- 

 vided with apophyses, and which forms a massive body, capable of but 

 a slight amount of movement ; in the other group, of which the 

 EcliinasteridcB, LincMadcB, Goniasteridce, Pterasferidce, and Astropec- 

 tinidce, are the more important forms, the " odontophore " is ordinarily 

 provided with apojihyses, and the adambulacral ossicles are not so 

 completely truncated. 



6. This classification accords with the results which M. Edmond 

 Perrier has gained from the study of the characters of the pedicel- 

 lariee, so far as they are present to afford assistance in this difficult 

 operation of arrangement. 



7. The teeth and the " odontophore " vary in form in the various 

 genera, and in many cases even in the various species. 



8. The so-called " odontophore " seems to be homologous with what 

 Miiller called the osseous peristomial plates of Euryaltis, and with 

 the corresponding parts in OpMura and Ophiocoma ; in extending his 

 survey to the Ecliinoidea, the author finds, as is natural, greater difii- 

 culties in his way, and he is content to insist on the morphological 

 resemblances presented by the "tooth" of the dentate forms (Des- 

 mosticha ; Casnidididce) when compared with the " odontophore " of the 

 starfish. 



No examination of any morphological characters in the Echino- 

 derma seems to be comjilete in these days which does not take into 

 account the corm theory of Haeckel, which, as we are informed by its 

 author, is " as yet the sole theory attempting the genetic explanation 

 of this remarkable group of animals ;" * and, indeed, the position and 

 the great value of the speculations of the German zoologist do demand 



* ' Evolution of Man,' Engl, tranil., ii. 480. 



