44 AEÏ. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



The trabecule are sparsely developed, without doid^t on 

 account of the narrowness of the space that they occupy. 



Chambers of the usual cup-like or thiml)le-like shape are 

 80-150 jjL wide. In a few instances it seemed to me that a 

 chamber freely communicated with a neighboring one through 

 the end which should normally l)e closed and rounded. 



Their wall or the reticular membrane exhi]:)its minute open 

 meshes not more than 11 n. wide (PI. III., tig. 11). Under a 

 moderately strong power of the microscope, the nodes of the 

 reticulum appear as swollen points somewhat more deeply coloretl 

 than the delicate Ijeams. Seen under the immersion-system the 

 choanocyte nucleus (about 2 //. dia.) is discernible not so much 

 by itself as by the fact that the spot is relatively clear of the 

 surrounding protoj^lasmic granules. It is scarcely stained by the 

 borax-carmine or the haematoxylin. In some of my preparations 

 the flagella is occasionally observable, though by no means in 

 a complete state. The collar is unrecognizable. 



Close to the thin oscular margin the ehaniber-laycr is re- 

 presented simply by the reticular membrane disposed in a conti- 

 nuous undulating manner instead of being formed into distinct 

 chambers (upper part of fig. 8). Superiorly, it finally ceases to 

 exist, its disappearance taking place insensibly in that its reticu- 

 lum gradually passes over into the wider-meshed cobwel) of the 

 ordinary trabecuUe (fig. 11). 



Well-stained arclueocytes, either isolated or grouped together 

 in varving numl)ei's, occur in abundance on the outer side of the 

 wall of the chambers, exactly as I have described in Eupledella 

 iiiarshaW (Contril). I., p. 1G5) and in Leucopmcus orlliodocus 

 (Contrib. III., p. 41). PI. III., fig. 11, shows two such groups 

 of quite insignificant size. The larger of the archœocyte-congeries 



