SIGNIFICANCE OF CERTAIN LARV/E OF ECHINODERMS. iSl 



Astcrina, and as is further demonstrated in the pluteus of Mcl- 

 lita, but that they possessed tentacles or assisted in capturing 

 food at this time is not, I think, supported by evidence. The 

 structure and function of the left hydroccele as an organ of lo- 

 comotion and feeding was, in my opinion, acquired during the 

 period of sedentary life after the animal had so increased in size 

 that ciliary action alone was not equal to the work of food 

 gathering. This point will be more fully discussed, however, 

 further on. 



To the bilateral ancestor as above described I would add, in 

 the place of the general coat of cilia with which it is usually pro- 

 vided, a locomotor and feeding apparatus consisting of five trans- 

 versely-placed ciliated rings and an apical tuft of sensory cilia. 

 The position of each is shown in Fig. 1 1 , a. 



Semon [ in his discussion of the larva of Synapta digitata con- 

 cludes that the transverse ciliated rings of both the holothurian 

 pupae and the larva of Antcdon are to be considered as secon- 

 dary structures. Lang 2 also states that it is not at all likely that 

 the ciliated rings (of echinoderm larvae) have any phylogenetic 

 significance. From the facts then available this was the only 

 conclusion warranted and its has been accepted almost without 

 exception by zoologists. It seems to me however that the ob- 

 servations recorded in this paper, which have been made since 

 the publication of the works of the authors just mentioned, make 

 it worth while to again call attention to the question and to dis- 

 cuss the bearing which the accumulated facts have upon our 

 conception of the structure and history of the hypothetical pelagic 

 ancestor of the echinoderms. 



Larvae such as Auricularia, Bipinnaria, Brachiolaria and 

 Plutei have never, to my knowledge, been seriously consided to 

 be primitive although the attempt to establish a relationship be- 

 tween echinoderms and Balanoglossus, on account of the general 

 similarity of the movements and external characters of the Auri- 

 cularia and Tornaria larvae, comes very near to an implied belief 

 in their primitiveness. In each of the above-mentioned larvae we 



'Richard Semon, "Die Entwicklung der Synapta digitata und die Stammesge- 

 schichte der Echinodernen." Jena Zeitschrift, Bd. XXII., 1888. 



2 Arnold Lang, "Text Book of Comparative Anatomy," p. 546. (Eng. trans.) 



