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that Heliocidaris erythrogramma has such a larva, although with only one 

 cihated band, might be adduced here as proving the occurrence of this 

 larval type also in Echinoids, where it was otherwise unknown. But it is 

 a very strong objection that in the whole class of the Asteroidea not one 

 case of larvae with ciliated rings is known, neither is anything correspond- 

 ing to the pupa-stage known in this class, which is otherwise one of the 

 more primitive of Echinoderms, at any rate more primitive than Ophiu- 

 roids and Echinoids. Another important fact is this, that in all the cases 

 where larvae with ciliated rings occur, the eggs are large and yolk-laden. 

 This evidently means that the larvae with ciliated rings, developing from 

 such eggs, are modified in accordance with the fact that they have food 

 enough in store in the yolk and therefore need not trouble with catching 

 food. The ciliated rings of these larvae decidedly would serve very badly 

 as food-gatherers. If that type of larvae were really the primitive form 

 we should have the remarkable fact here of an organism having arisen 

 evidently unable to subsist by its own means. The fact that the stage 

 with the ciliated rings is never indicated in the beginning of the larval 

 development, but always at its end in those forms which have larvae of 

 the typical pelagic shape, is also very hard to understand on the assump- 

 tion that the form with the ciliated rings is the more primitive. Also the 

 fact that in the viviparous Ophionotus hexacUs the embryos develop into 

 larvae corresponding exactly to the generalized, primitive type of Echi- 

 noderm-larvae, is of considerable importance in this connection ; this larva 

 decidedly needs no special adaptation to pelagic life, and it is hard to see 

 why it should adopt this form instead of that with the ciliated rings, were 

 it not of phylogenetic importance. 



In my opinion there is then no doubt that the larva with a simple 

 circumoral band, as it is found in the younger stages of all the four 

 main larval types of Echinoderms, is the primitive form, and that it 

 represents a true phylogenetic stage in the ancestry of Echi- 

 noderms — that is to say, the larva in its simplest type, the Dipleu- 

 rula. Of course, the larvae of recent Echinoderms, with their more or 

 less highly specialized characters, do not represent ancestral types of the 

 various classes of the Echinoderms, Bipinnaria of the Asteroids, Echino- 

 pluteus of the Echinoids etc. They represent special adaptations of the 

 original pelagic ancestral form, having been modified along with the 

 adults, so as to form groups corresponding with the natural groups of the 

 adults, the result being that there is a larval classification exactly parallel 

 with that of the adults. But the primitive type, the Dipleumla must I 

 have no doubt, represent the organism from which the whole of the 

 Echinoderm stem developed. 



