RAYS AND BILATERAL SYMMETRY 267 



because of his wide range of observations relative to this point, 

 must sutHce. In summarizing what is known on the subject 

 with reference to the Asterids, he says, '89 (p. 418): "The 

 water pore and hydrocoel occupy their usual positions, but the 

 latter remains open to the anterior enteroccel, from which it 

 probably arises." And as a more general statement (p. 420) : 

 " The water pore always (with the possible exception of Holo- 

 thurians) arises in connection with the posterior end of the left 

 anterior enteroccel, and only communicates indirectly, if at all, 

 with the hydrocoel." 



While quoting Bury on this point, however, it would be unfair 

 to his views not to mention that he believes the distinction 

 between the anterior enteroccel and hydrocoel to be a deep-seated 

 one. It is, at the same time, interesting to find him remarking 

 in connection with the development of these parts in Echinids 

 that " a stage is soon reached in which, but for the evidence 

 afforded by Ophiurids, the fundamental distinction between the 

 anterior enteroccel and the hydrocoel could hardly have been 

 recognized" (p. 413). 



And while calling attention to the close morphological rela- 

 tion that exists between the enteroccel of the preoral lobe and 

 the hydrocoel ; in other words (to translate the statement into 

 phraseology that would apply more strictly to post-larval life) 

 between the cavity of the peduncle of the late larva and young 

 adult in many species, and the water-vascular system, attention 

 should also be called to the manner in which this peduncle is so 

 frequently used. Thus, Ludwig, '82, p. 154, declares that, 

 " Die Larve benutzt, wie das schon von dem ersten Beobachter, 

 Lacaze-Duthiers, richtig gesehen worden ist, das Larvenorgan 

 in ganz ahnlicher Weise, wie des Seestern seine Saugfiisschen." 



Turning to the paper (Lacaze-Duthiers, '74) referred to by 

 Ludwig in this quotation, we do not find that the French author 

 expressly compares the use made of the larval organ by the 

 larva of Asteriscus {Astertna P) which he studied, with the 

 ambulacral tentacles of the star-fish ; he does, however, after 

 giving a lively account of the movements of the larva, speak of 

 its adhering to foreign bodies by the peduncle " par une sorte 

 de succion" (p. 29). 



