376 SOME ZOOLOGICAL METHODS. 



P or if era. 



749. Spongiae : Fixation. The smaller forms (Calcispongiae) 

 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 ascer- 

 tain. 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 Spongilla) besides absolute alcohol an alcoholic sublimate 

 solution, and the liquids of Kleinenberg and Flemming, with 

 good effect. 



Staining. On account of the great tendency to maceration 

 above referred to, I hold (notwithstanding many recommen- 

 dations of watery stains that are to be found in the literature 

 of the subject) that alcoholic stains be alone employed 

 for staining sponges, and I particularly recommend Mayer's 

 tincture of cochineal as giving the best results known 

 to me. It is better than Kleinenberg's haematoxylin for 

 this purpose, because hsematoxylin tends to make the tissues 

 brittle. 



Sectioning. Calcareous sponges may be decalcified in 

 alcohol slightly acidified with hydrochloric acid, and then 

 imbedded in the usual way. Siliceous sponges may be desi- 

 licified by Mayer's hydrofluoric acid method mentioned, ante, 

 541. But in view of the really dangerous nature of this 

 operation, I feel bound to recommend that it be avoided. 

 Fair sections may be obtained from sponge tissues well im- 

 bedded in paraffin without previous removal of the spicula. 

 The spicula appear to be cut; probably they break very 

 sharply when touched by the knife. Of course you will not 

 use your best knives for cutting such sections. 



Preparation of Hard Parts. Siliceous spicules are easily 

 cleaned for mounting by treating them on a slide with hot 

 concentrated nitric or hydrochloric acid, or solution of potash 

 or soda. The acids mentioned are very efficient, but it must 



