CHAPTER XXXVI. 525 



Small forms are very easily prepared by means of osmic acid. For 

 the large forms see Lo BIANCO, loc. tit., p. 457. He uses his copper 

 sulphate mixture, 987. 



SAMASSA makes sections by the double-embedding method. See 

 Arch. mik. Anat., xl, 1892, p. 157. 



992. Plankton, Preservation of, without Sorting (E. J. ALLEN and 

 E. T. BROWNE in Science of the Sea. John Murray. 1912). Pre- 

 servation of whole catch of a tow-net is performed by stirring 

 around the Plankton with a rod and adding a little 5 to 10 per cent, 

 formalin. Keep on stirring for about a minute, then allow the 

 organisms to settle to the bottom ; as soon as this occurs pour off 

 as much of the liquid as possible and transfer the Plankton to a 

 bottle ; again allow to settle and reduce the fluid to a minimum ; 

 then fill the bottle with 5 or 10 per cent, formalin. A bottle should 

 be not more than half full of Plankton. After a few days, or on the 

 appearance of opalescence of the fluid, change the liquid. Another 

 method is first to fill the Plankton by pouring some saturated solu- 

 tion of picric acid into the jar containing the organisms, then add 

 some formalin 5 or 10 per cent, and leave for an hour or two, 

 occasionally stirring. Finally decant and add 5 or 10 per cent, 

 formalin as before described ; the yellow colour of the fluid can be 

 neglected. Never use corrosive sublimate with formalin, as crystals 

 form, which adhere to the organisms. 



Porifera. 



993. Spongiae : Fixation. The smaller forms can be fairly well 

 fixed by the usual reagents, osmic acid being one of the best. For 

 the larger forms absolute alcohol is apparently the best. If any 

 watery fluid be preferred, care should at all events be taken to get 

 the sponges into strong alcohol as soon as possible after fixation, on 

 account of the rapidity with which maceration sets in in watery 

 fluids. FIEDLER (Zeit. iviss. ZooL, xlvii, 1888, p. 87) has been using 

 (for Spongilla), besides absolute alcohol, an alcoholic sublimate 

 solution and the liquids of Kleinenberg and Flemming. 



Staining. To avoid maceration, I hold that alcoholic stains should 

 be alone employed, and I recommend Mayer's tincture of cochineal, 

 235. VON LENDENFELD (Zeit. wiss. Mik., xi, 1894, p. 22) uses 

 aqueous solutions of Congo red and anilin blue for the coloration of 

 collar-cells. 



MINCHIN (Quart. Journ. Mic. Sci., xl, 1898, p. 569) stains spicula 

 sheaths with Freeborn's picro-nigrosin, 742. 



