NOTOCRINUS VIUILIS. 51 



preservation in alcohol. In the thin part of the ectoderm only some few 

 small nuclei lie close to the surface and glandular cells are seen only here and 

 there (plate xxvi, figures 4 and 5). The ectoderm of the vestihulary invagi- 

 nation differs from the ectoderm of the outer side only in being niucli thicker 

 (plate XXV, figures 1 to 6). 



The bottom of the furrow is richly provided with glandular cells in the 

 part from a little below its anterior end to about where the hydroccel begins. 

 But there is no such shifting of the glandular and the nuclear parts as was 

 described for Isomeira vivipara. In the figures on plate xxv the glandular 

 parts are not shown. The reason for this is that they have been drawn from 

 sections stained with hematoxylin, in which the glandular parts are not 

 clearly defined; but in other sections, stained with picrocarmine, the glandu- 

 lar parts are very distinctly differentiated by being of a clear yellow color, 

 while the nuclei are stained beautifully red. 



There is a very distinct ciliation in the furrow (plate xxvi, figure 10). 

 The cilia are seen to perforate the cuticula; inside the cuticula is seen a 

 darker line, not a series of fine grains, as was observed in Isometra (plate 

 XVII, figure 5). 



From the sections represented in plate xxv, figures 1 to 6, it would appear 

 that the closure of the furrow is about to begin at the anterior end. I do 

 not think this conclusion justified. The narrowness of the outer part of the 

 furrow seen in figure 3 is evidently due to accidental pressure and is not found 

 in other specimens. 



The nervous system is remarkably developed for a larva apparently not 

 in special need of it, being devoid of both the power and opportunity for 

 movement. The nervous system must here be just a morphological remi- 

 niscence. It is forming a conspicuous layer below the epidermis in the anterior 

 end (plate xxvi, figure 6), reaching almost as far downwards as to the 

 posterior end of the vestibulary invagination. Ventrally it is more restricted 

 and is seen only below the suctorial disk (plate xxv, figure 1); from here it 

 branches (plate xxv, figure 2) and may then be followed for some distance 

 downwards as a distinct nerve along each side of the vestibulary invagination. 



The entoderm forms a wide sac with thin walls, with the nuclei arranged 

 in a layer of somewhat varying thickness, in many places even in a single 

 regular layer (plate xxiv, figures 4 to 9; plate xxv, figures 4 to G). The 

 lumen of the entoderm sac is entirely empty; there is no trace of yolk or 

 inwandering cells in it. 



The Injdroccel is a half ring, lying in the normal place a little to the left 

 of the vestibulary invagination (plate xxiv, figures 5 and 9; plate xxv, 

 figures 5 and 6). The primary tentacles are just beginning to appear, as 

 indicated by the thickenings of its epithelium seen in plate xxvi, figure 1. 

 Also a slight prolongation towards the parietal canal — not seen in any of 

 the figures, as no section was favorable for showing it — probably indicates 

 the beginning formation of the stone canal. The pore canal is closed (plate 



