MATERIALS FOR A MONOGRAPH OF THE ASCONS. 475 



and cytoplasm are concerned, most excellently, and has the 

 great advantage of not acting upon the spicules or corroding 

 tliera in any way ; though should it be required to remove the 

 spicules, the specimens can easily be decalcified by adding a 

 little hydrochloric acid either to the glycerine or to the alcohol, 

 without the stain being in the least affected thereby. The 

 nucleus is shown up very distinctly in the cells, and as a rule 

 nothing else but the nucleus is stained by the picrocarmine. 

 But in the case of granular nuclei the finer structure of the 

 framework and chromatin elements is not well shown by this 

 method, which gives an evenly stained nucleus, exhibiting 

 only traces of granulation ; and hence for nuclear studies this 

 method requires to be supplemented by others. Vesicular 

 nuclei, on the other hand, are very well shown. The difficulty 

 with which we have to contend in Ascon histology is that all 

 methods which show good nuclear detail, require fixing fluids 

 which are more or less strongly acid, and such fluids act, of 

 course, upon the spicules. The best preservative I have found 

 for the nuclear structures in these forms is Flemming's fluid, 

 but its application causes the spicules to dissolve rapidly, with 

 abundant evolution of gas, as the result of which the tissues 

 may be mechanically injured. Moreover the collar-cells are 

 not nearly so well preserved by Flemming^s fluid as by the osmic- 

 picrocarmine method, at least as regards collar and flagellura. 

 Absolute alcohol is a preserving agent much employed for 

 sponges, but I have not found it very good for Ascons. The 

 general structure of the cells is not so well preserved by the 

 method already mentioned, while the nuclei often have their 

 structure altered and deformed by it. It has, however, the 

 advantage of preserving the spicules. 



Since I propose in the present memoir to discuss only the 

 general histological structure as seen in preparations made by 

 the osmic-picrocarmine method, and to leave the discussion of 

 finer cytological details for a subsequent paper, I will not con- 

 sider further here the action of the various fixatives and stains. 



Sponges preserved with osmic and picrocarmine are often 

 more or less macerated, especially if the osmic has been 



