CHAPTER XXV. 285 



624. Removal of Membranes. It may often be advisable not to 

 attempt to remove them, but to soften them with eau de Javelle or 

 eau de Labarraque. See 545. 



MORGAN (Amer. Natural., xxii, 1888, p. 357) recommends (for 

 the ova of Periplaneta) eau de Labarraque diluted with 5 to 8 volumes 

 of water, and slightly warmed. This will soften the chitin mem- 

 branes sufficiently in thirty to sixty minutes, if employed before 

 fixing. Fixed ova take longer. The fluid must, of course, not be 

 allowed to penetrate into the interior of the ovum. 



625. HENKING'S Methods (Zeit. wiss. Mik., viii, 1891, p. 156).- 

 HENKING generally kills ova by plunging them into hot water, or 

 by pouring hot water on to them in a watch-glass, and then removing 

 into 70 per cent, alcohol. 



He thinks that eau de Javelle for softening membranes is best 

 avoided. They should either be dissected away or left in situ, and 

 cut with the rest of the egg, according to the nature of the case. To 

 avoid brittleness of the yolk proceed as follows : After fixing and 

 treating with alcohol, prick the chorion and stain with borax- 

 carmine. Put the stained ova for twelve hours into a mixture 

 containing 20 c.c. of 70 per cent, alcohol, 1 drop of concentrated 

 hydrochloric acid, and a knife pointful of pepsin (it is not necessary 

 that all the pepsin should be dissolved). The ova may then be 

 treated with alcohol, oil of bergamot, and paraffin, and (with some 

 exceptions, amongst which is Bombyx mori) will be found to cut 

 without crumbling. 



626. Diptera (HENKING, Zeit. wiss. Zool, xlvi, 1888, p. 289). 

 Ova still contained within the fly may be fixed by plunging the 

 insect for some time into boiling water, then dissecting out and 

 bringing them into 70 per cent, alcohol. Laid eggs may have 

 boiling water poured over them, or be put into solution of Flemming 

 in a test-tube which is plunged into boiling water until the eggs 

 begin to darken (about a minute). Cold solution of Flemming easily 

 causes a certain vacuolisation of the contents of the ova. Open 

 the ova at the larger end, stain with borax-carmine for fifteen to 

 thirty hours, and cut in paraffin. 



BRUEL (Zool. Jahrb., Abth. Morph., x, 1897, p. 569) fixes larvae 

 and pupae in absolute alcohol heated to 70 to 75 C., and con- 

 taining a ' little ' sublimate. See also VAN REES, ibid., iii, 

 1888, p. 10. 



BENGTSSON (Handl. Fysiogr. Scellsk Lund., viii, 1897) finds hot 

 alcoholic solution of sublimate (Frenzel's, 69) the best fixative for 



