668 PROF. MINCHIN ANB DR. REID ON THE [June 16, 



The same combinations of acids and stains were also applied to 

 the spicules placed on the slide in water, without any albumen. 

 When treated in this way, the sheath of the sj)icule stains so 

 deeply as to largely obscure the axial filament, either on account 

 of the spicule being exposed on all sides to the action of the stain, 

 or because the prepai^ation does not go through the processes of 

 washing and clearing necessary for a permanent preparation, 

 processes which probably extract a certain amount of the colour. 

 The deep colour of the sheath is especially marked in the combina- 

 tions with nitric, hydrochloric, and acetic acids, more so than 

 with picric acid. The fact that the sheath stains so intensely is 

 of interest, since it shows that the action of Eau-de-Javelle in 

 isolating the sponge-spicules does not destroy the sheath. When 

 the spicules are fixed to the slide with albumen, each spicule 

 appears after treatment with the combined acid and stain as a 

 space or movild in the layer of albumen limited by a deeply- 

 stained contour (compare fig. 1, PI. XXXIV., fig. 5, PI. XXXY., 

 and fig. 8, PI. XXXVII. especially) ; but since the albumen takes 

 the stain also, the sheath cannot be distinguished with certainty 

 as a structure separate from the enveloping albumen, in spicules 

 fixed in this way. The fact that the spicule-sheath is not dis- 

 solved in Eau-de-Javelle is in favour of Biitschli's view that the 

 sheath is chiefly inorganic in nature ; a conclusion founded by 

 him on the observation that the sheath could be isolated by means 

 of caustic potash (357o)j though this reagent dissolved the rest of 

 the spicule, and that sheaths so isolated were dissolved by strong- 

 acetic acid. 



When the processes of decalcification and staining were watched 

 under the microscope, it was observed that the picric acid com- 

 binations did not break up the spicules so much as the othei- 

 acids, even when these were used in strengths much lower than 

 those quoted above. With picric acid and nigrosin combined, the 

 filament appears first at the tip of the ray, and as the decalcification 

 goes on, the filament appears as if traced by the tip of the gradually 

 receding calcite, initil it reaches the centre, when decalcification 

 is complete. With hydrochloric and nitric acid combinations the 

 decalcification does not go on so regulaily ; fragments of the 

 spicules are frequently seen to be cut off fi'om the rest of the 

 spicule, and when separated, the fragments rush along to the 

 tips of the rays as if impelled by powerful currents. The violence 

 of the action of the acid was most marked with hydrochloric, 

 less with nitric, and least with acetic acid ; it pi-obably accounts, 

 for the fact that the axial filaments are not, as a rule, so well 

 shown with these acids as with the picric-acid combinations. 



In addition to the combinations of acids and stains mentioned 

 above, many experiments were made with acids and stains used 

 separately. When clean spicules, placed in distilled water on the 

 slide vvithoui: any albumen, were treated with acids, it was usually 

 observed, especially when acetic acid was used, that the whole 

 spicule seemed to disappear, leaving only the axial thread, without- 



