584 E. A. MINOHIN. 



Fig. 11 . — Triradiate system showing one ray fully formed and the other 

 not yet so. In the former ray the basal formative cell is at the apex of the 

 spicule as the definitive spicule-cell ; in the latter it is still not far from the 

 base of the ray. 



Fig. 12. — Triradiate system not quite full-grown ; the rays are conical in 

 form, and the formative cells still contain numerous granules. In the case of 

 one ray the formative cell is quite at the base ; in the case of the other it 

 has begun to migrate towards the apex. 



Fig. 13. — Triradiate system showing what is apparently an apical formative 

 cell just detached from one of the rays at an unusually late period of its 

 growth. The basal formative cell in this ray has travelled halfway to the 

 apex ; that on one of the other rays is still at the base. 



Fig. 14. — A fully formed spicule ray, showing the spicule cell at the 

 extreme edge. 



PLATE 39. 



Figs. 15 anb 16. — Clathrina coriacea. 



Fig. 15. — A porocyte in process of immigration from the flat epithelium, 

 near a triradiate system. Dermal aspect. One portion of the cell has 

 definite limits and an indented outline, and lies at a deeper level, in 

 contact with the collar-cells. The other portion is spread out without 

 clearly defined limits, and is quite superficial. The cell shows a large 

 vacuole containing apparently calcareous matter, spicule remnants. 

 Near the cell lies what appears to be a fragment of a broken spicule. 

 Fig. 16. — Surface view of the dermal epithelium, with a porocyte in 

 process of immigration. For the latter compare description of last 

 figure. 



Figs. 17— 21.— Clathrina, sp. dub. 



Fig. 17. — Surface view of dermal layer from dermal aspect, showing three 

 cells of iiat epithelium, two spicule rays, one bearing a spicule-cell, two 

 minute wandering cells, and a sextet of spicule-forming cells. The 

 spicule has not as yet appeared. 



Fig. 18. — A young quadriradiate surrounded by formative cells. Gastral 

 aspect. The rays of the basal system are surrounded by a sextet of 

 formative cells. The minute gastral ray is contained in a porocyte 

 containing two nuclei, one close to the ray in question. 



Fig. 18a. — The porocyte and spicule of the last figure drawn separately 

 from the other cells. 



Fig. 19. — View of dermal layer, gastral aspect ; collar-cells removed. 

 The figure shows twelve cells of the flat epithelium ; several spicules 

 and spicule rays, one of which shows a single spicule-cell at its 



