NOTES ON ECHINODERM MORPHOLOGY. 



383 



displaced towards the next radius (figs, i, iii, w.p.). The water- 

 pore of the Asterid larva has precisely the same relation to one 

 of the genital plates (fig. iv, w.p.). When it first appears it does 

 not communicate only with the hydrocoel, as it does in the later 

 larvse and in the adult, but with, the left division of the 

 enteroccel, from which the hydroccel eventually originates. In 

 the Crinoid this condition is the permanent one. The primary 

 water-pore and the numerous pores subsequently developed all 

 open into that part of the body cavity which is developed from 

 the left peritoneal tube. Rhizocrinus has but one in each inter- 

 radius ; but this is not the case in the allied genus Bathycrinus, 

 which has several, and also several water-tubes depending into 

 the enterocoel from the oral ring. The aberrant genus Hi/ocrinus 

 presents some singular variations in this respect. 



In both the specimens which I have examined there are two 

 pores in the oral plate of the anal interradius, and there are no 

 others in any of the anambulacral plates which lie between it and 

 the edges of the radials. This is interradius No. 1 of Ludwig's 

 Asterid nomenclature. 



In the other interradii the disposition of the water-pores is as 

 follows : 



Thus, therefore, one specimen has all the oral plates perforated 

 by water-pores, with one possible exception ; while in the other 

 it is only in the anal interradius and in the next beyond it 

 which contains the fore-gut (No. 5) that the oral plate is 

 pierced by a water-pore. It is significant that this interradius 

 (No. 5) is that in which the primary water-pore appears in 

 larval Asterids, Ophiurids, and Crinoids ; and also that in both 

 the specimens of Eyocrinus the water-pore is a little beyond 

 the middle line of the large oral plate, just as in the larvse 

 described by Ludwig. I am bound to admit that these facts 

 may be thought to support Ludwig's theory, but I do not 

 think that they do when considered by the light of its results. 



The point on which I lay stress, as Ludwig seems to do also, 

 is the radiate symmetry of the animal. If a Crinoid and Starfish 



