THE DEVELOPMENT OF OPHIOTHRIX FRAGILIS. 563 



oesophagus. Carpenter (7) was chiefly occupied iu estab- 

 lishing a fanciful homology between the dorsal plates of 

 Amphiura squamata and the aboral plates of a Crinoid. 

 My own work (17) had reference to the first origin of the 

 genital cells, and dealt solely with post-larval stages. I dis- 

 criminated for the first time between various spaces which 

 had been confused under the name '^ axial sinus." The 

 problematical organ lying along the stone-canal, which had 

 been regarded as a heart by some zoologists, was shown to be 

 of peritoneal origin, and to represent the first rudiment of the 

 genital cells. This paper contains one serious blunder wliich 

 I endeavoured to set right in my paper on Aster iua gib- 

 bosa (18), viz. the vesicle representing the right fellow of the 

 hydrocoele is confused with a space originating as a peri- 

 toneal invagination and labelled in my figures Sinus b. 



Reviewing the narrative so far given, it will be seen that 

 the only two investigators who advanced our knowledge of 

 the early larval stages of Ophiuroidean development were 

 Miiller and Metschnikoff. To these it is now necessary to add 

 a third name, viz. that of H. Bury. This talented investi- 

 gator, who gave to zoology the first satisfactory account (4) 

 of the development of the Crinoid Antedou rosacea, was 

 led by his study of this species to revive the idea of a meta- 

 meric segmentation of the Echinoderm larva. Taking up the 

 investigation of the larva3 of other classes of Echinodermata, 

 he found his ideas amply confirmed, and in 1889 he published 

 a paper (5) in which he showed that a transverse division of 

 the coelom took place in the larvas of both Echinoidea and 

 Ophiuroidea. Bury was the first to discriminate an anterior 

 coelom from the hydrocoele, which he regarded as an essen- 

 tially unpaired organ. This hydrocoele, as he showed, was 

 formed comparatively late in development, and arose as an 

 outgrowth from the left anterior coelomic vesicle iu Echinoidea, 

 whilst in Ophiuroidea he felt himself compelled to assert that 

 it was an outgrowth from the left posterior vesicle. During 

 the interval between the appearance of the papers of 

 Metschnikoff and Bury quite a number of authors had made 



