266 RITTER AND CROCKER 



sition of the two organs, and point out certain facts of develop- 

 ment that seem to us to give considerable probability to the con- 

 jecture that future study will discover some closer relation 

 between them than that of mere chance correspondence in 

 position. 



The facts to which we refer concern the relation of the hy- 

 drocoel to the anterior coelom, which is the enterocoel of the 

 larval organ, in the larva, and the method by which the water 

 pore and stone canal communicate with these cavities. 



Ludwig, '82, pointed out that in Asierina gibbosa, while the 

 dorsal pore is not formed until after the hydrocoel begins to dif- 

 ferentiate itself from the enterocoel, it yet does not at first com- 

 municate directly with the incipient hydrocoel, but rather wdth 

 the left enterocoel, so that for a considerable time the hydrocoel 

 communicates with the exterior only by way of the enterocoel. 

 And from these facts the author is led to declare : " Nur scheint 

 es demnach den Thatsachen besser zu entsprechen, wenn man 

 den Riickenporus in seiner primaren Bedeutung als einen in 

 den Enterocoel fiihrenden Porus betrachtet, w^elcher erst sekun- 

 dar in engere Beziehung zu dem von dem Enterocoel abge- 

 spaltenen Wassergefas^systeme tritt " (p. 144). 



As development goes on, the anterior enterocoel, i. e,, here 

 the enterocoel of the larval organ, becomes distinctly set off from 

 the left posterior enterocoel, though for a long time remaining in 

 communication with it, and it is not until on the tenth or eleventh 

 day, when the metamorphosis is so far advanced that several 

 pairs of ambulacral tentacles have appeared on the radial canals 

 and the adult star is distinctly blocked out, that the coelom of the 

 larval organ is finally severed from the water vascular system, 

 as the larval hydrocoel has now become. 



These observations of Ludwig's have been fully confirmed, 

 so far as the essential particulars are concerned, by later inves- 

 tigations, MacBride, '96, in fact, aflirming that "the conjoined 

 tubes (/. (?., stone-canal and pore-canal) still open to the anterior 

 coelom, and this opening persists in the adult, a fact which Lud- 

 wig did not observe" (p. 362), 



Numerous other citations of like import might be given ; but 

 one or two from Bury to which special weight must be attached 



