1892.] and Spongoblasts in one of the Keratosa. 135 



Schulze's detailed description .... particularly in Euspongia, 

 I am persuaded that tbe ectoderm cells of the horny sponges are of 

 the same form and character as those in the Homocoela." By apiece of 

 good fortune I am now able to state that this is so. In a sponge 

 found at Naples, which appears to me to correspond fairly with 

 0. Schmidt's Gacospongia scalaris, the ectodermal elements are quite 

 plainly to be seen even with a low power ; indeed in the specimen 

 examined their arrangement is more regular, invariable, and easy to 

 observe than in any sponge that I have yet investigated. 



FIG. 1. 



50 



Scale of u>. 



EC tod erm> Cells of Cacospongia : , sp. 



The cell-bodies are shown focussed through the silver-lines ; the neck of each 

 cell lies towards the upper part of the figure; it is at the same focus as the surer 

 area, in the middle of which its granules lie on the outer surface. 



Dilute osmic acid, followed by nitrate of potash and nitrate of silver. 



The cells in question are of a flask-shaped form,, very slender, elon- 

 gated, and thin-necked. I have been able most successfully to de- 

 monstrate their relations to the silver areas (fig. 1), to prove without 

 doubt that they open on the surface in the centre of those areas 

 and not in any interstices between them, to prove also equally with- 

 out doubt that each silver area Las no nucleus connected with it 

 except the one lying in the base of the pendent cell body (" subdermal 

 gland-cell " of authors), and thus to justify completely the inability 

 of Schulze and other trustworthy investigators to find nuclei at a 

 more superficial level, where the " flat epithelium " was usually sup- 

 posed to exist. 



In this sponge the spongoblasts of the primary fibres form a con- 

 tinuous tissue with the ectoderm cells and resemble them indistin- 

 guisbably both in form and character ; a brief discussion of previous 

 observation on this point will be found in the paper already quoted. It 

 is nearly impossible at least, for my inexperience to give the effect 

 of a three-dimensional preparation except by a most elaborate draw- 

 ing, but the outlines given in figs. 2 and 3 will render some idea of 

 the appearances on which I base this statement. The impression 



