EMBRYOLOGICAL METHODS. 343 



piece of liver by passing an entomological pin through the 

 albumen, then incises the albumen and turns out the ova 

 into fixing liquid. 



MICHAELIS (Arch. mik. Anat., xlviii, 1896, p. 528) fixes 

 ova in a mixture of concentrated sublimate solution and con- 

 centrated picric acid, twenty parts each, glacial acetic acid 1, 

 and water 40, but removes the envelopes before bringing into 

 alcohol. 



603. Salamandra (RABL, Morphol. Jahrb., xii, 2, 1886, p. 

 252). For his more recent methods see 587. 



604. Rana (0. HKRTWIG, Jen. Zeit. f. Naturw., xvi, 1883, 

 p. 249). The ova are thrown into nearly boiling water 

 (90 to 96 C.) for five or ten minutes. The albuminous 

 envelope of the ovum is then cut open, and the ovum ex- 

 tracted under water. The ova are then brought into 0'5 

 per cent, chromic acid for not more than twelve hours, or 

 into alcohol of 70, 80, and 90 per cent. Chromic acid 

 makes ova brittle and attacks the pigment, whilst alcohol 

 preserves it, which is frequently important for the study of 

 the germinal layers. 



MOKGAN (Amer. Nat., xxv, 1891, p. 759 ; Journ. Roy. Mic. 

 Soc., 1892, p. 284) has the following. During the periods 

 in which it is difficult or impossible to remove the inner jelly- 

 membrane the eggs can be freed as follows : Each egg is 

 cut out with scissors from the general jelly-mass, and put 

 for from one to twelve hours into saturated solution of picric 

 acid in 35 per cent, alcohol containing ' ' the same amount of 

 sulphuric acid as in Kleinenberg's solution." Wash for 

 several hours in several changes of alcohol, beginning with 

 35 per cent., and increasing the strength gradually up to 70 

 per cent. About the second day in the 70 per cent, alcohol 

 the inner membrane begins to swell, and on the third or 

 fourth day may be pierced by a needle, and the egg removed 

 and placed in 80 per cent, alcohol (see also WHITMAN, Meth. 

 of Research, p. 156 ; and SCHDLTZE, Zeit. f. wiss. ZooL, xlv, 

 1887, p. 177). 



605. Sulphate of Copper Hardening Liquid (FoL, Lehrbuch, p. 106, 

 after REMAK and GOETTE) ; for hardening ova of Amphibia : 



