136 Mr. G. Bidder. On the Flask-shaped Ectoderm [June 16, 



FIG. 2. 



Exterior. 



Protruding 

 Horn-fibre . 



Cuticle. ^ v r? ., 



Horn-fibre 



out of focus 

 within the body 

 of the sponge. 



Ectoderm Cells at the apex of a conulus of Cacospongia sp. (Focus near the 

 surface of the skin.) 



The shading is diagrammatic ; the dark shading indicates apparently naked horn- 

 fibre, the light shading horn-fibre covered with living tissue. 



FIG. 3. 



Horn -fib 

 within the bod 



of the sponge. 



Protruding 

 Horn-fibre. 



Cuticle. 



Spongoblasts near the apex of a conulus of Cacospongia sp. (Focus near the 

 profile of the fibre. Slightly smaller scale than fig. 2.) 



Figs. 2 and 3 are from the same preparation, prepared with osmic acid, picro- 

 carmine, and glycerine. 



given is that the apex of a conulus is a locus of attraction for ecto- 

 deim cells, and that the fibre is nothing more than the concentrated 



