SOME METHODS FOR LOWER ANIMALS. 489 



vessel half full of 6 to 8 per cent, form oh The formol, being 

 lighter than sea water, diffuses up into the tube in about an 

 hour, and kills the animals in extension and with little loss 

 of the swimming-bells ; after which they may either be pre- 

 served in the formol itself, or be further hardened with other 

 reagents. 



876. Ctenophora : Fixation. The small forms are very easily 

 prepared by means of osmic acid. For the large forms see 

 Lo BIANCO, loc. cit., p. 457. 



SAMASSA has succeeded in making sections of Ctenophora 

 by means of the double-imbedding method, 166 (see Arch. 

 /. mik. Anat., xl, 1892, p. 157 ; Zeit. /. wins. Mik., 1893, 

 p. 340). 



Porifera. 



877. 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 no satisfactory fixing agent has 

 yet been discovered, so far as I can ascertain. The tissues 

 of this group are very watery, very delicate, very friable after 

 hardening, and macerate with the greatest facility. For all 

 but very small specimens, absolute alcohol is apparently the 

 best fixing agent. 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. f. wiss. ZooL, xlvii, 1888, p. 87) has been using 

 (for Spongilld), besides absolute alcohol, an alcoholic subli- 

 mate solution and the liquids of Kleinenberg and Flemming 

 with good effect. 



Staining. On account of the great tendency to maceration, 

 I hold that alcoholic stains should be alone employed for 

 staining sponges, and I particularly recommend Mayer's tinc- 

 ture of cochineal, 230. VON LENDKNFELD (Zeit.f. wiss. Mik., 

 xi, 1, 1894, p. 22) uses aqueous solutions of Congo red and 

 &nilin blue for the coloration of collar-cells. 



Sectioning. Calcareous sponges maybe decalcified in alcohol 

 slightly acidified with hydrochloric acid, and then imbedded 



