392 . DR ARTHUR T. MASTERMAN ON THE 



considerable advance has been made internally. Histologically, there is still remarkably 

 little progress. The epiblast still remains the same columnar epithelium, the mesenchyme 

 presents the same reticular structure, and the epithelium of the various organs is the 

 same as in the last stage, with the exception of the greater thickness of the mesenteron. 

 Figs. 92 to 100 give a series orientated as in the former series of stage E, i.e., horizontal 

 longitudinal to larva and through radius 3 of the adult. 



In fig. 96 the small aperture from the hypogastric coelom still leads into the basal 

 part of the pre-oral coelom dorsally to the stone-canal ; the pre-oral coelom now consists 

 of a small basal part, the axial sinus, connected by a long canal or neck to the more 

 spacious part still persisting in the pre-oral lobe. Eadius 5 of the hydrocoele shows the 

 first pair of tube-feet and the radial vessel clearly defined. In fig. 97 the dorsal sac 

 is seen to be quite separated from the anterior coelom, and to be (also in figs. 98 and 99) 

 alongside of the pore-canal. Close to its anterior (larval) border is the tip of the 

 hypogastric coelom ; in figs. 81 and 82 these two parts are seen to be in close proximity, 

 and here they actually touch. Recalling to mind Goto's statement that the dorsal sac 

 in Asterina arises from this process of the hypogastric coelom (or posterior coelom), it is 

 well to notice this contiguity here, and the manner in which it is produced. A com- 

 parison of figs. 97 and 98 shows that the neck or canal of the pre-oral coelom is now 

 lying in a bay or groove on the termination of the hypogastric coelom, which is pushing 

 round both orally and aborally. At the oral end of the axial sinus is the perihsemal 

 cavity 4/5 growing orally as a crescentic process (cf. fig. 98). We may note the very 

 close approximation of the two ends of the hypogastric ccelom, which are now only 

 separated by the breadth of the axial sinus in the inter-radius. 



Fig. 98 shows the passage between mesenteron and hypogastric coelom just closing, 

 whilst the epigastric ccelom also comes into view. In fig. 99 two consecutive tube-feet 

 of radius 3 are cut, their fellows being seen in fig. 102 ; four tube-feet are also present 

 in 2 and 1. The hypogastric ccelom is seen to be giving off the perihsemal coelom 4/3 

 growing orally to the hydrocoele ring, as in fig. 100. Aborally to this is the oral 

 coelom (MacBride) arising as a process in inter-radius 4/3 from the hypogastric coelom. 

 Another rudiment of the oral coelom is seen in fig. 101 as a similar process protruding 

 between mesenteron and hydrocoele in inter-radius 5/1, another in fig. 103 growing out 

 into inter-radius 2/1, and in the same figure a fourth growing out into inter-radius 2/3. 

 In other words, the oral coelom arises at this stage from four inter-radial processes 

 from the hypogastric ccelom, each corresponding in position (aborally thereto) to the 

 respective four perihsemal processes. There is at this stage no trace of the element of the 

 oral coelom corresponding to inter-radius 5/4, the hypogastric coelom being absent from 

 this inter-radius. MacBride and Goto find the oral ccelom originating from the hypo- 

 gastric coelom, but, so far as I am aware, do not remark upon its origin from inter-radial 

 elements in Asterina or Asterias pallida. The perihsemal elements 5/4 and 4/3 have 

 been noticed : fig. 101 shows the commencement of 5/1 ; fig 102 shows 3/2 well advanced ; 

 and 2/1 is seen in figs. 103 and 104. Like the bydroccelic radii, the perihsemal 





