ACANTHASCUS CACTUS. 155 



diameter varies from 90/^ to 190/^. The chamber wall I have 

 seen as a reticular membrane witli 02:>en meshes (PL XI., fig. 19). 

 The choanocyte nuclei, though scarcely differentially stained as 

 they lie in the nodes of the reticulum-forming granular protoplasm, 

 can at places be distinctly recognized as svich. They are of about 

 the same size as the trabecular nuclei. None of the preparations 

 are such as to allow anything to be said about the flagellum or 

 the collar. 



On the outside of, and in close ap])Osition to, the chamber 

 wall are variously sized groups of well-stained archœocyies reach- 

 ing up to 3i !>■ in diameter. A small group of the same is seen 

 in PL XL, fig. 19, on the left. The archaïocytes lie close 

 together, generally arranged in a single layer Hat upon the 

 chamber wall or between the walls of directly adjacent chambers. 



The trabecidce, both external and internal, are as usual 

 cobweb-like. Their nuclei, measuring about 1 !'■ in diameter, are 

 well-stained and contain generallv more than one chromatic 

 granule. 



Along the lumen of the larger canals, both incurrent and 

 excurrent, the trabecuUe are at places extensively exjmnded into 

 a thin lining film, so that they might be spoken of as constituting 

 here a canalar membrane. 



The dermal membrane (see PL XL, fig. 18, left) is film-like 

 j^erforated by large and small "pores" of roundish or oval shape. 

 The parts between closely adjoining "pores" may be reduced to 

 mere threads indistinguishable from the trabecula3. Not only does 

 the essential agreement in histological nature but also the fact 

 that the same thesocytes and microdiscohexasters occur in both 



