580 E. W. MACBRIDE. 



statement on views of living larvse. Now^ fig. 42 h shows that 

 the }3ore is opposite the interval between lobes 4 and 5, and 

 if one were to imagine that the stone-canal led vertically 

 downwards beneath the pore one would conclude that it must 

 open between lobes 4 and 5. With regard to the other 

 groups of Echinoderms, the evidence at present to hand 

 certainly does suggest that the opening is placed in a different 

 inter-radius from that in which it opens in Asteroidea and 

 Ophiuroidea, but until this point has been thoroughtly investi- 

 gated by means of sections it would be premature to give up 

 the hope that the rest of Echinoderms may be shown to 

 agree in this respect with these two groups. The intestine, 

 as fig. 41 shows, is a loose, baggy structure in the Ophio- 

 pluteus larva. The anus is kept closed, except during the 

 emission of fa3ces ; the cells lining the intestine differ in tone 

 and size from those lining the stomach, these latter being 

 more cylindrical and staining more deeply than those lining 

 the intestine. 



The Metamorphosts. 



In the case of the larva of Asterina gibbosa the meta- 

 morphosis may be said to begin from the moment that the 

 larva fixes itself. At this period the hydrocccle is an open 

 hoop with five lobes, which are just beginning to show them- 

 selves externally by causing protrusions of the ectoderm. In 

 the case of the larva of Echinus esculentus and that of 

 Ophiothrix fragilis, which remain swimming until the 

 metamorphosis is complete, it is impossible to fix in such a 

 way a definite point which indicates the beginning of the 

 change. In the larva of Asterina gibbosa, when it has 

 just fixed itself, the hydrocccle is an open hoop ; one may, 

 therefore, regard the beginning of metamorphosis in the larva 

 of Echinus esculentus as marked by the acquisition of 

 lobes by the hydrocoele, which is at first a hoop but almost 

 immediately passes into the ring form. In Ophiothrix 

 fragilis, where the lobes appear whilst the hydrocccle is 

 still straight, metamorphosis mny be regarded as begun, by 



