54 AKT. ~—I. IJI3IA : HEXCÏINELLIDA, IV. 



the inner cellular mass at tliis stage difter^ in no way from that 

 of a simi^le archseocyte-congeries. 



The spicules appear shortly after, in embryos of 110-130/^ 

 diameter, in the same shape and j^osition as I have described for the 

 same embryonal stage oï Leucopsacus orthodocii^ (Contrib. III., p. 44). 

 (Bee PI. III., figs. 10 & 17). They are all minute oxystauract- 

 ins and are situated in the ])eriphery of the inner mass and at 

 a short distance from its limit against the external epithelium. 

 They are distributed, widely apart from one another, in a single 

 Jayer running parallel to the external contour of the spherical 

 I.Mxly. The plane of the foui- rays in each spicule coincides with 

 that of the layer and is therefore slightly concave on the inner 

 side. In the earliest developmental stage of the oxystauractius 

 (fig. 17) that I have seen, the axial length mersured 1~) u.. The 

 central node was flat and disc-like and was j'clatively large in 

 comparisoii with the small spiiie-like rays. I did not succeed in 

 bringing the axial iilaments into view, nor could any of the 

 cells directly adjoining the spicules l)e distinguished from the 

 rest as scleroblasts. It is most unsatisfactory that the spicules 

 could not 1)0 observed at the very beginning of their develop- 

 ment. For such minute observations the methods I have used 

 seem to have been inadequate. 



»Some time after the appearance of the spicules, the eml)ryo- 

 nal ])ody l)egins to elongate and assumes for a time an ovoid shape. 

 1*1. III., fig. 18, shows an endjryo in this stage of development. 

 It is ajjparently in longitudinal section, but I am not in a position 

 to slate exactly the direction in which it had been cut, since it 

 was ibund in the wall of the mother sponge which had been sectioned 

 without any knowledge of its presence. As it appears on the 

 section in question, the flagellated layer invests the body on 



