142 I. IJIMA : HEXACTINELLIDA. I. 



in addition to the flagella proper, the lateral contour-lines of the 

 collai's and that the shorter lines in the sketch stand for these. I 

 regret that I have had no opportunity to renew my observations 

 on fresh specimens. 



I have of course not neglected to try silver- nitrate methods 

 on fresh specimens with the view of demonstrating cell-outlines 

 in the chamber- wall. The methods referred to browned the 

 protoplasm but always failed to bring out the expected boundary 

 lines. Not only this negative result, but also the perfectly con- 

 tinuous appearance of the substance constituting the reticular 

 beams, strongly inclines me to believe that the memhrana reticularis 

 represents, so to say, a fenestrated syncytial layer, — in other words, 

 that the individual choanocytes stand in organic fusion with their 

 fellows by the aforesaid beams or the lateral protoplasmic processes. 

 And I think this is not a i^henomenon that stands quite alone 

 in the group of the Spongida taken as a whole. For, it will be 

 conceded b}^ all that the reticular beams of the Hexactinellidan 

 chamber-wall correspond in all probability to those protoi^lasmic 

 processes which are known to extend radially from the bases of 

 choanocytes in a number of other sponges. For several species 

 of the Calcarea {Ascetta priviordialis, Sycandra raphanus, Vosmaeria 

 corticata), R. v. Lendenfeld ('92) has stated that these processes 

 anastomose and form a network. Sollas ('88, p. xxxvill) 

 has also made the statement, I suppose for the Spongida generally, 

 that the same continuously unite each choanocyte with its sur- 

 rounding fellows. 



The structure of the chamber-wall and of the single choano- 

 cytes as described by me in the above unfortunately does not 

 accord in some important points with the description given by 



