590 E. W. MAOBllIDE. 



such larva3 are only captured when the tow-net is dragged 

 along the bottom. Soon the animal rests on the bottom 

 altogether, and then the ciliated epithelium is rapidly 

 absorbed, leaving sometimes, as fig. 17 shows, a portion of 

 one of the calcareous rods, which it originally covered, as a 

 bare, projecting spine. The arms of the young Ophiurid 

 are armed at the sides with hooks. These hooks strongly 

 resemble the hooks which form the sole armature of the arms 

 in such primitive genera as Ophiohelus, and it is interesting 

 to find them recurring in the biephic stage of Ophiothrix. As 

 a matter of fact these hooks persist in this genus throughout 

 life, but as growth proceeds there is added to each one of 

 them a vertical row of those delicate, thorny, lateral spines 

 from which the genus takes its name. 



Comparison of the Development of Ophiothrix with that 

 OF other Echinoderms. 



Before discussing the bearing of the facts which have just 

 been laid before the reader, it is proper that a word or two 

 should be spoken as to the difference between my i-esults and 

 those of Dr. Caswell Grave on Ophiura brevis (12). Some 

 of these differences, such as the rapid development, are attri- 

 butable to the fact that Ophiura brevis has yolky eggs 

 and never develops a typical Ophiopluteus larva ; but others 

 are of greater import. The origin of the coclom, as two dis- 

 tinct evaginations from the archenteron, of Avhich the hinder 

 forms the hydrocoelc and the left posterior coclom, is un- 

 paralleled among Echinoderms. We can only venture to 

 suggest that, as Dr. (Irave distinctly states that he had only 

 an exceedingly limited su]iply of material, that his interpreta- 

 tion of the appearances presented to him is mistaken, owing 

 to stages being missed out. 



It is true Mastermau has announced somewhat similar results 

 in the case of CribreUa oculata (20). Here, according to 

 him, the coclom originates as two evnginations, of which one 

 gives rise to the single anterior crrloin, characteristic of 



