272 EMBRYOLOGICAL METHODS. 



Arthropoda. 



581. Fixation of Ova. In most cases the ova of Arthropods 

 are fixed by heat in a more satisfactory way than by any other 

 means. This may be followed either by alcohol or some 

 watery hardening agent. 



582. Removal of Membranes. This is frequently very difficult, 

 and it may often be advisable not to attempt to remove them, 

 but to soften them with eau de Javelle or eau de Ldbarraque 

 (see the methods of Looss and LIST). 



MORGAN (Amer. Natural., xxii, 1888, p. 357; Zeit.f. wiss. 

 Mik., vi, 1, 1889, p. 69) recommends (for the ova of Peri- 

 planeta) eau de Labarraque diluted with five to eight volumes 

 of water, and slightly warmed. Thus used, it will soften the 

 chitin membranes 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. 



583. Lepidoptera (BOBEETZKY, Zeit. f. wiss. ZooL, 1879, p. 

 198). Ova (of Pieris cratdegi and Porthesia chrysorrhoea) are 

 slightly warmed in water and put for sixteen to twenty hours 

 into 0*5 per cent, chromic acid. The membranes can then be 

 removed, and the ova brought for a few hours into absolute 

 alcohol, stained with carmine, and cut. 



584. Phryganida (Neoplialax) and Blattida (PATTEN, Quart. 

 Journ. Mic. Sci., 1884, p. 549). The ova or larvae are placed 

 in cold water, which is gradually raised to 80 C. You leave 

 off heating as soon as the ova have become hard and white. 

 Pass very gradually through successive alcohols, beginning 

 with 20 per cent. ; stain with Kleinenberg's haematoxylin, or 

 Mayer's cochineal (only alcoholic stains will traverse the 

 chorion) . The ova may remain in the haomatoxylin for five 

 or six days, and be washed out in alcohol containing one drop 

 of HC1 per 20 grammes, in which they should remain for 

 several days, and then be soaked in pure alcohol until they 

 have regained their violet colour. Penetrate with benzol and 

 imbed in paraffin. 



587. Diptera (HENKING, Zeit.f. wiss. Zool., xlvi, 1888, p. 289 ; 

 Zeit. f. wiss. Mik., 1889, p. 59). Ova still contained within 



