GENERAL PART 



I. Classification. 



AFTER the description given above of the new larvae reared or other- 

 . wise gathered it now remains to see, whether this material, together 

 with that known from previous researches, gives any answer to the original 

 question, which was the guiding principle in the author's studies, namely 

 this: is there any correspondance between the different larval forms and 

 the natural groups of the adult forms — or to put it more definitely: is 

 there a larval classification corresponding to that of the adult forms, each 

 group of the adults (genus, family or order) having a distinct type of larvae 

 differing from that of the other groups? 



It is known already from Joh. Miiller's magnificent researches that 

 at least each class of Echinoderms has its own distinct larval type — the 

 Holothurians the Auricularia, the Asteroids the Bipinnaria, the Ophiu- 

 roids the Ophiopluteus and the Echinoids the Echinopluteus^), the Crinoids 

 alone having no separately named larval type, which is also unnecessary 

 as long as we do not know a single case of a typical pelagic Crinoid-larva. 

 But are "orders" and "famihes" to be distinguished within these four 

 larval types? The question may at once be answered, at least partly, in 

 the affirmative. A more detailed discussion is, however, necessary. 



Starting with the Echinoid-larvEe it was clear already from the pre- 

 vious researches that the Spatangoid-larvae form a very distinct type, char- 

 acterized by the unpaired posterior process, which does not normally occur 

 in any of the other Echinoid-larvae, so far as hitherto known^). They also 

 differ from all other Echinoid-larvae in having well developed anterodorsal 

 arms. We now know the larvae of quite a number of Spatangoids, viz. of 



1) Joh. Muller designated both the Ophiurid- and the Echinoid-larvse simply as Plu- 

 teus ; the separation of these two larval types under the names of Echinopluteus and Ophio- 

 pluteus was introduced in the present author's work "Die Echinodermenlaven d. Plankton- 

 Expedition." 



^) Prouho in his "Recherches sur le Dorocidaris papillata" (Arch, de Zool. exp6r. g6n6r. 

 V. 1888) describes and figures (p. 141, PI. XXV, fig. 9) an abnormal larva of this species 

 with an unpaired posterior process. 



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