190 I. IJIMA : HEXACTINELLIDA. I. 



Hexacfcinellida, and to give to the generality of archseocyte-con- 

 geries a physiological significance in accordance therewith. How- 

 ever, some important points may possibly have escaped my 

 attention in tracing the origin of the embryo, since the supply 

 of materials for the investigation of the points in question was 

 not as plentiful as might be desired. I sliould therefore prefer 

 to defer the definite formulation of an opinion until after I have 

 had more opportunities for studying the matter than I have had 

 hitherto. 



Summaries of the Histology of 

 E. marshaUi. 



Chamber-wall : 



1. The choanocyte has a flattened, ramified body, con- 



taining a likewise flattened nucleus. It possesses a 

 collar and a long flagellum. 



2. The collar is narrow, approximately cylindrical, and 



stands out quite isolated from its neighboring fellows. 



3. The ramifications or lateral processes of the choanocyte- 

 body are fused with one another so as to form the 

 reticular membrane. 



4. All the meshes of the reticular membrane are open 



and serve as prosopyles. 

 o. The reticular membrane has on its external side 

 neither a basal membrane nor a layer of connective 

 tissue to rest upon. In it are inserted only the ends 

 of the external trabecule which keep the chambers 

 expanded and in position. 



