E. MAESHALLI. — FLAGELLATED CHAMBER. 166 



A relation similar to that between the reticular and the 

 marginal membrane in the chamber-wall seems to be repeated 

 in the tracsition of the chamber-layer into the general trabecular 

 system. Such a transition should occur around every osculum, 

 where the chamber-layer must have termination. In Eupledella 

 I have not been able to bring this termination into view, probably 

 in consequence of the complicated folding of the layer close to 

 the oscular edge. Whereas, in certain Hyalonematids and 

 Rossellids it was not difficult to determine on both sections and 

 surface-views that, close to the thin oscular edge, the chamber- 

 layer was represented by an irregularly undulating, continuous 

 sheet of the reticular membrane, whose reticulation finally be- 

 came merged into, and indistinguishable from, that of the trabe- 

 cular system. 



The reticular membrane, or as it has been called by F. E. 

 ScHULZE the membrana reticularis (PL V, figs. 36-43), forms one 

 of the most characteristic features in the organisation of the 

 Hexactinellida. It consists of peculiar choanocytes whose flattened 

 and ramified bodies, in my opinion, join with one another to 

 constitute an extremely thin and delicate layer of minutely meshed 

 network. When seen under a microscope of moderately high 

 power, the reticulation presents an elegant and tolerably regularly 

 checkered pattern. Uuder a very high power, the pattern loses 

 in appearance much of its regularity. The meshes, though mostly 

 quadrate, are frequently trapezoidal, rhomboid or triangular in 

 shape, with usually rounded corners. The sides measure 3-7 /« in 

 length. 



From all that I have seen of the reticular membrane not 

 only in Euplectella but also in a series of Hyalonematid, Rossellid 



