ECHINODERMATA 415 



however, from the beginning exists only as an indistinct appendage of the 

 hydrocoele; likewise in the Crinoidea (Antedon) only an anterior entero- 

 coele is present, which, united with the hydrocoele, is constricted off 

 from the archenteron. What Bury here considers as anterior enterocoele 

 and hydrocoele together, other authors look upon as hydrocoele only. 

 Where the conditions are of such a character as they are in the Holo- 

 thurioidea and Crinoidea, and to some extent in the Asteroidea, Bury 

 conceives a partial degeneration of the originally paired and segmentally 

 arranged enterocceles. 



It is not to be denied that in most forms the common entero-hydrocoele, 

 the so-called vaso-peritoneal vesicle, communicates (by means of the 

 dorsal pore) with the outside world ; but whether it was the enterocoele 

 alone which originally possessed this union, and whether the hydrocoele 

 was united with it only secondarily, does not yet seem to be proved by 

 Bury's investigations as long as the origin and subsequent fate of his 

 anterior and posterior enterocoeles remain unknown. 



III. THE DEVELOPMENT OF THE TYPICAL LARVAL 



FORMS. 



Having become acquainted with the most important pro- 

 cesses which take place within the body of the larva, we 

 turn to the consideration of its external shape. This is very 

 different in the separate groups of Echinoderms. Like 

 MtJLLER, we start with a simple fundamental form, from 

 which to derive the different larval forms. This funda- 

 mental type is an elongate, oval to pyriform larva, which is 

 somewhat flattened on the ventral side. This larval form 

 arose from the gastrula, the blastopoi^e of which is meta- 

 morphosed into the anus, while the archenteron bends 

 around toward the ventral side and here connects with 

 the outside world by means of the larval mouth. The larva 

 possesses still another opening in addition to these two, 

 namely, the dorsal pore of the water-vascular system. The 

 flao-ella with which the larva was at first uniformly covered 

 disappear in part, and are retained only on limited areas, 

 which are called ciliated bands. 



Crinoidea. — The larva of Antedonis one of the most sim- 

 ply constructed of Echinoderm larvae. At first of fairly uni- 

 form, oval shape, it is subsequently slightly curved toward 

 the somewhat flattened ventral surface. In place of the com- 



