THE DEVELOPMENT OF OPHIOTHEIX FEAGILIS. 567 



of the anterior and epigastric (right posterior) coelomSj but lias 

 an independent origin from the gut ; in this case, however, the 

 hydrocoele is derived from the anterior coelom. In both cases we 

 have to do with yolky eggs and a shortened development, and 

 in both cases a re-examiuation of the facts is desirable, as Grave 

 would be the first to admit, since throughout his paper he 

 laments the scantiness of his material and the gaps between 

 the stages. It is to be hoped that he will be able at no 

 distant date to give the whole subject a thorough revision. 



Mortensen in 1898 published a systematic review of all the 

 forms of Echinoderni larva? known up till that date (22). In 

 this valuable paper he discusses the homology of the various 

 larval appendages, and introduces a nomenclature which will 

 bo employed in this paper. Auother service which he has 

 rendered is to introduce the terms Ophiopluteus and 

 Echinopluteus for the larva? of Ophiuroidea and Echino- 

 idea respectively, thus doing away with the confusion implied 

 in the use of the term " Pluteus." In a second paper (23) he 

 makes an addition to the number of varieties of Echinoderm 

 larva3 known, and with this second paper our review of the 

 knowledge so far gained may be said to be complete. 



Material and Methods. 



In the summer of 1898, whilst I was staying at Plymouth 

 investigating the development of Echinus esculent us, I 

 received a large number of specimens of Ophiothrix 

 fragilis, which appeared to be sexually ripe. I therefore 

 attempted artificial fertilisation, but as the developing egga 

 remained at the bottom I concluded that they were abnormal. 

 About eight days afterwards, to my delight, I found a certaiu 

 number of perfectly formed, free-swimming larvae in the jar. 

 These larvte continued to develop, and at the end of twenty- 

 six days had completed their metamorphosis. The jar in 

 which the larvtB were placed was shaded from the light and 

 fitted with a Browne plunger. During the summer of 1898 

 the Phytoplankton was particularly abundant, and so the de- 



