no ANATO^IV AXn DEVELOPMENT OF THE ECHIXODERMS 



As in the Annelid-larvje patches of cilia are frequently developed 

 elsewhere than in the principal circle, e.g. on the sides of the body, at 

 the bases of the feet, &c., so .in the Echinoderms, ciliated elevations 

 and circles (not encircling the body), and even long processes {Echinus, 

 Brachiolarid), are developed upon other parts of the body of the larva 

 than the " ciliated fringe." 



In the Echini and Ophiuridse these additional parts are developed 

 in the post-trochal'region (Diag. I., II., III. [Plate 12]) ; in the Asteridse 

 they are as invariably developed in the pre-trochal region (Diag. IV., 

 v., VI. [Plate 12]). 



The ciliated circle of the Ophiurid-larva on the dorsal side of the 

 post-trochal region answers precisely to the ciliated " band " on the 

 dorsal side of the pre-trochal region of the Asterid-larva. 



We have ventured here to give a general view of the Echinoderm- 

 larva; different from that put forth by Prof Miiller himself, who, we 

 would with all deference suggest, loses sight of the real position of the 

 ciliated fringe in its apparent bilaterality. Speaking of the ciliated 

 fringe he says, " We may name this circular ciliated fringe (VVimper- 

 schnur), to distinguish it from such as encircle the body transversely, the 

 bilateral ciliated fringe" (Metam. d. Holothurien u. Asterien, p. 35). 



We maintain that this " bilateral " fringe itself does, in truth, en- 

 circle the body transversely, however distorted it may have become, 

 and the reader is referred to the diagrams for a demonstration of the 

 truth of this position. 



A strong confirmation of this opinion is afforded by the structure 

 of the larva of Sipunculus described by Max. Miiller (Miill. Archiv, 

 1850, v.). (Fig. 8.) 



In this remarkable larva there is a single even band of strong cilia 

 which encircles the anterior part of the animal, and evidently repre- 

 sents the " ciliated fringe " of the other Echinoderm-larvae. Except 

 that the intestine is bent upon itself, it agrees precisely with our hypo- 

 thetical type of the Echinoderm-larva. 



The Echinoderm-larva, we repeat, may be considered as an Anne- 

 lid-larva, which has become distorted by the excessive development 

 of the dorsal part of its post-trochal region.^ 



Out of these larvae, all of which have a strictly bilateral symmetry, 



1 The only other animals which possess a larva at all resembling that of the Echinoderms 

 and Annelids are certain Trematoda (see Miiller, Ueber eine eigenthumliche Wurmlarve 

 aus der Classe d. Turbellarien, Miill. Arch. 1850). Here it would appear that by an 

 excessive development of the pre-trochal region, the ciliated fringe has the concavity of its 

 bend posterior ; but the difficulty, from the absence of an anus, of determining the real axis 

 of the body, renders this determination doubtful. 



