216 AETHUE DENDY. 



the Melbourne University, who kindly made a careful exami- 

 nation of it for me, with the following results. The granules 

 were scraped into a glass, dried, stained with fuchsin, mounted 

 in Canada balsam, and examined under a J^_inch oil im- 

 mersion objective (Leitz) with a No. 5 eye-piece. We 

 then found that they presented the appearance shown in fig. 

 58, being usually each somewhat dumb-bell shaped, or com- 

 posed of two ovoid segments placed end to end, though 

 sometimes the shape was irregular. They averaged about 

 0'004 mm. in length, and consisted of a fairly darkly stained, 

 sometimes slightly granular body, with a round very darkly 

 staining structure, presumably a nucleus, in each end of the 

 dumb-bell, or, when the shape was irregular, with several such 

 nuclei. It thus appears that, though probably not bacteria, 

 the bodies in question are micro-organisms of some kind 

 which live upon the surface of the ectoderm. Nuclei, pre- 

 sumably belonging to the epithelial cells, are still visible 

 amongst the granules, at any rate in the inhalant canals, and 

 I am inclined to think also on the outer surface of the sponge; 

 but we have here an excellent illustration of the way in which 

 the structure of the ectoderm is sometimes obscured by the 

 accumulation of foreign bodies. 



Bidder would possibly interpret the subdermal gland-ceils 

 of Grantiopsis cylindrica as representing the true ecto- 

 dermal epithelium. But they do not look like it (fig. 56). 

 They appear to be but very slight modifications of the ordinary 

 stellate mesodermal cells, and as such they will be described 

 on a future page. 



The Endoderm. 



I have little to add concerning the histology of the endo- 

 derm to what I have already written on the subject. As already 

 stated, I consider as endoderm not only the collared cells 

 which line the flagellated chambers, but also the flattened 

 pavement epithelium which lines the gastral cavity and ex- 

 halaut canals of the Heterocoela. It is, of course, quite 

 conceivable that tliis pavement epithelium is formed by an 



