CHAPTER XXV. 267 



by means of two pins on the bottom of a dissecting dish, with the 

 mesometrial surface downwards and the ovular eminence upwards. 

 The dissecting-dish is then filled up with serum or liquid of MULLER, 

 or 0-1 per cent, solution of osmic acid, Bouin's fluid, Hill's fluid, 

 Helly's fluid or 10 per cent, formol. See sections on " Cytology," 

 673 to 696. With a small scalpel a longitudinal incision is made 

 on the surface of the ovular eminence, not passing deeper than the 

 muscular layer ; the underlying uterine mucosa is then gently 

 dilacerated with two pairs of small forceps, and the ovum set free 

 in the liquid. 



From the moment the 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.) 



RETTERER (C. R. Soc. de BioL, 1887, p. 99) advises that for ova 

 of the seventh day the segment of uterus containing them be opened 

 on the 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. 



C. Gr. HARTMANN (Jour. Morph., 1916), in his study of the develop- 

 ment of the opossum, used Carney's, Bouin's, Fleming's and Hill's 

 fluids. He found Hill's " Marsupial mixture " a perfect fixing fluid 

 for marsupial eggs. J. P. Hill now recommends leaving out the 

 acetic acid for delicate objects. 



589. Blastoderms and Later Embryos. The routine methods of 

 embryology apply here in general. Great care must be exercised 

 to avoid rough treatment caused by upgrading the object too 

 quickly. The same remark applies even more particularly to clear- 

 ing, which to get the best result should be done very gradually. 



In order to bring out the outlines of blastoderm cells the living 

 ovum may be brought into ^ per cent, 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. The preparations thus obtained are 



