8 Prof. Muller on the Anatomy and Development 



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, Brachiolaria) , are developed upon other parts 

 of the body of the larva than the u ciliated fringe." 



In the Echini and Ophiuridse these additional parts are deve- 

 loped in the post-trochal region (Diag. I. II. III.) * in the Aste- 

 ridse they are as invariably developed in the pre-trochal region 

 (Diag. IV. V. VI.). 



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

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

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



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

 derm- larvae different from that put forth by Professor Muller 

 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 cir- 

 cular ciliated fringe (Wimper-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 u bilateral u fringe itself does, in truth, 

 encircle the body transversely, however distorted it may have 

 become, and the reader is referred to the diagrams for a demon- 

 stration of the truth of this position. 



A strong confirmation of this opinion is afforded by the struc- 

 ture of the larva of Sipunculus described by Max. Muller (Mull. 

 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 represents the u ciliated fringe " of the other Echino- 

 derm-larvse. Except that the intestine is bent upon itself, it 

 agrees precisely with our hypothetical type of the Echinoderm- 

 larva. 



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

 Annelid-larva, which has become distorted by the excessive deve- 

 lopment of the dorsal part of its post-trochal region*. 



Out of these larvae, all of which have a strictly bilateral sym- 

 metry, the more or less radiate adult Echinoderms are developed 

 by a process which is a sort of internal gemmation. 



Now the result of this process is twofold ; either the new 



* The only other animals which possess a larva at all resembling that of 

 the Echinoderms and Annelids are certain Trematoda (see Muller, Ueber 

 eine eigenthumliche Wurmlarve aus der Classe d. Turbellarien, Mull. 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 bod v. renders this determination doubtful. 



