DIPTERA. 319 



be soaked in pure alcohol until they have regained their 

 violet colour. Penetrate with benzol and imbed in paraffin. 



WHEELER (Journ. of MorpTi., iii, 1889, p. 292 ; Journ. Roy. 

 Mic. Soc., 1890, p. 250) dissects out ovarian ova in salt solu- 

 tion and fixes in liquid of Perenyi (fifteen minutes), then 

 treats with alcohol, and stains with borax-carmine. Laid 

 eggs may be killed by Patten's method. After heating, the 

 two lips of the crista of the capsule may be separated with 

 fine forceps and pieces of the walls torn away, and the eggs 

 pushed out of the compartments formed by their choria and 

 hardened as desired. Good results are also obtained by 

 heating to 80 C. for ten minutes in liquid of Kleinenberg, 

 and preserving in 70 per cent, alcohol. This causes the en- 

 velopes to dilate and stand off from the surface of the egg, 

 so that they can easily be dissected away. 



CHOLODKOWSKY (Mem.Acad.Imp. /S^.PetersZmr^xxxviii, 1891 ; 

 Zeit. f. wiss. Mik., ix, 1, 1892, p. 80) recommends cutting off 

 the ends of the cocoons and fixing for twelve hours in liquid 

 of Perenyi, or for a few minutes in a solution of 1 part iodine, 

 1 part iodide of potassium, and 300 parts water, heated to 

 boiling-point. 



HEYMONS (Zeit. f. wiss. ZooL, liii, 1892, p. 434; Zeit. f. 

 wiss. Mik., ix, 3, 1893, p. 343) finds that Cholodkowsky's 

 methods are good for the study of general relations of parts, 

 but not satisfactory for the preservation of delicate detail. 

 For young embryos it is better to incise the cocoon at the end 

 by which it inheres in the body of the mother, bring it for 

 two minutes into water heated to 90 C., and open in Flem- 

 ming, in which the embryo should be dissected out. 



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

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

 the fly may be fixed by pluoging the animal 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-car- 

 mine for fifteen to thirty hours, and cut in paraffin. 



