EMBRYOLOGY 367 



805. Uterine Eggs, During the fourth, fifth, and sixth days 

 after copulation the ova of the rabbit are free in tlie uterine 

 cornua ; they are easily visible to the naked eye, and may be 

 extracted by the same manipulations as those of the tubes. After 

 the sixth day they are at rest in the uterus, but have not yet 

 contracted adhesions with the mucosa, so that they can still be 

 extracted whole. At this stage the parts of the cornua where the 

 ova are lodged are easily distinguishable by their peculiar aspect, 

 the ova forming eminences of the size of a pea. The cornua should 

 be cut up transversely into as many segments as there arc 

 eminences, care being taken to have the ova in the centre of the 

 segments. You then fix each segment 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 osmie acid, Bouin's iluid. Hill's fluid, Helly's 

 fluid or 10 per cent, formol. See sections on " Cytology," §§ 691 

 to 714. 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. G. Hartmann {Journ. Morph., 1916), in his study of the 

 development of the opossum, used Carnoy's, Bouin's, Flcniming'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 ascetic acid for delicate objects. 



806. Blastoderms and Later Embryos. The routine methods of 

 embryology apply here in general. Great care must be exercised 



