METHODS OF IXVESTIGATIOX. 33 



made most plainly observable when the spicule is inclosed in 

 glycerine, in dammar, in tlie acid in wliicli it was boiled, or in 

 fact in any medium whose refractive index equals or nearly 

 equals that of the siliceous matter. 



For the histological study of soft parts I have tried, when- 

 ever oppoi'tunities offered themselves, to preserve samples of the 

 various Hexactinellids in special waN's. Since Eupleclella mar- 

 shalli was the most readily accessible species, my experiments 

 with different reagents and my subsequent study of the soft 

 tissues were mainly conducted on that species. 



Right at the spot of capture and as soon as the sponge 

 came up to the surface, it was received directly into a bucket 

 while still iu the sea. It was tlien immediately cut up into small 

 pieces, whicb were thrown at once into the several reagents. 

 The latter were contained in tubes or bottles supplied with an 

 elevated false bottom in order to facilitate the rapid replacement 

 of the sea-water by the killing fluid. I have used utmost des- 

 patch in these processes to make sure of the reliability of the 

 results. However, certain experiences have led me to think that 

 with proper precautions — i. e., by keeping them in the dark, 

 cool, quiet, and in a plenty of good sea-water, — the soft tissues 

 remain for some hours in about the same condition, tliougli not 

 in as active a state of life, as when first brought up from the 

 sea-bottom. Hence, opportunity is gis-en us of examining com- 

 paratively fresh tissues in the laboratory. 



With fresh objects thus brought home I have repeatedly 

 tried silver (Hakmer's method) and Methylenblau (Mayer's 

 method) impregnation ; but never once have I been able to 

 bring out cell-outlines either on the trabeculse or on the chamber- 

 wall. 



