EMBRYOLOGICAL METHODS. 293 



From the moment tlie ova have become adherent to the 

 uterine mucosa they can no longer be extracted whole. The 

 embryo being always situated on the mesometrial surface, the 

 ovular eminence is opened by a crucial incision, and the strip 

 of mucosa to which the embryo remains adherent is fixed 

 with pins on the bottom of the dish. ED. v. BENEDEN (see 

 Arch, de Biol. } v, fasc. iii, 1885, p. 378) has been able by 

 operating in this way in serum of Kronecker, and keeping 

 the whole at blood temperature, to observe the circulation 

 of the embryo for hours together. (If this be desired to be 

 done, the crucial incision should not be too extended, so as 

 to leave the terminal sinus intact.) 



RETTEKER (C. R. Soc. de Bwl. y 1887, p. 99) advises that 

 for ova of the seventh day the segment of uterus containing 

 them be opened on tin 1 mesometrial surface, for at that date 

 no adhesion has yet been contracted with that side. By 

 running in liquid of Kleinenberg by means of a pipette 

 between the ovum and the free surface of the uterus, the 

 ovum may be got away in the shape of a closed vesicle. 



For the study of living eggs (of Rats and Mice) see MARK 

 and LONG, Cont. Zool. l<a!>. Mus. Comp. Zool. Harvard Coll., 

 1912, No. 225 (description of constant temperature chamber 

 and circulation slide). 



592. RABBIT ; Microscopic Preparations.- In order to make 

 permanent preparations of the different stages of fecundation 

 and segmentation, v. BENEDEN (Arch, de Biol., i, I, 1880, 

 p. 149) brings the living ovum into a drop of 1 per cent, osmic 

 acid on a slide, and thence into solution of Miiller (or 

 bichromate of ammonia or solution of Kleinenberg). After 

 an hour the liquid is changed, and the whole is put into a 

 moist chamber, where it remains for two or three days. It 

 is then treated with glycerin of gradually increasing strength, 

 and at last mounted in pure glycerin acidified with formic 

 acid. Ova may be stained after careful washing. 



In order to bring gut the outlines of blastoderm cells the 

 living ovum maybe brought into one third percent, solution 

 of nitrate of silver. After remaining there for half a minute 

 to two minutes, according to the age of the vesicle, it is 

 brought into pure water and exposed to the light. 



After the end of the third day the blastodermic vesicle 



