490 CHAPTER XXXIV. 



in the usual way. Siliceous sponges may be desilicified by 

 Mayer's hydrofluoric acid method (see 574). 



For ROUSSEAU'S methods see 558, 574. VOSMAER and. 

 PEKELHARING decalcify with a solution of picric acid in abso- 

 lute alcohol (see Zeit. f. u-iss. Mik., xv, 1899, p. 462). 



See also Johnstone-Lavis and Vosmaer, 174. 



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 

 be pointed out that they will attack the silex of some delicate 

 spicules. Thus DEZSO found that the small stellate spicules 

 of the cortex of Tethya lyncurium are completely dissolved 

 by boiling hydrochloric acid. Potash solution is, therefore, 

 frequently to be preferred, notwithstanding that, in my ex- 

 perience, it does not give such clean preparations. 



According to NOLL, eau de Javelle is preferable to any of 

 these reagents (see 555). 



Impregnation with Silver (see 343) . 



Embryos and Larvae. MAAS (Zool. Jahrb., Abth. Morph., 

 vii, 1894, p. 334) fixes larvae in liquid of Flemming or Her- 

 mann, one to three minutes, and stains with borax-carmine, 

 or with gentian violet and Orange Gr (Flemming). 



DELAGE (Arch. Zool. Exper., x, 1892, p. 421) fixes larvae of 

 Sponyilla that have settled down on cover-glasses for three 

 minutes in absolute alcohol, stains in alcoholic carmine, 229, 

 and brings through alcohol into oil of bergamot, then either 

 mounts direct in balsam, or detaches the larvae from the 

 cover and imbeds in paraffin (three minutes). 



Protozoa. 



878. Introductory. Since the Protozoa may be considered 

 as free cells, it is evident that the reagents and methods of 

 cytology are in great part applicable to this group. One of 

 the most generally useful of these reagents will be found in 

 the acid solution of methyl green ; it is the reagent that allows 

 of the readiest and best demonstration of the presence and 



