RABBIT. 307 



living ovum may be brought into one third 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 pre- 

 parations thus obtained are instructive, but blacken rapidly, 

 and cannot be permanently preserved. 



After the end of the third day the blastodermic vesicle can" 

 be opened with fine needles, and the blastoderm washed, 

 stained, and mounted in glycerin or balsam, v. Beneden 

 has also obtained good preparations by means of chloride of 

 gold. 



For embryonic areas and more advanced embryos Kolliker 

 recommends putting the ovum into 0*5 per cent, solution of 

 osmic acid until it has taken on a somewhat dark tint, 

 which happens in about an hour, and then treating it with 

 successive alcohols for several hours. If the ovum be ad- 

 herent to the uterine mucosa the portion of the membrane to 

 which it is fixed should be left, stretched out with pins, in 

 O'l per cent, solution of osmic acid for from four to six hours. 

 The blastodermic vesicle can then easily be removed, and 

 immersed for a few hours more in 0'5 per cent, solution of 

 osmic acid, and finally be brought into alcohol. For sections 

 Kolliker fixes with osmic acid. v. Beneden treats the ova 

 for twenty -four hours with I per cent, solution of chromic 

 acid, then washes well, and brings them through successive 

 alcohols. Chromic acid has the advantage of hardening 

 thoroughly the vesicle, and maintaining at the same time 

 the epiblast-cells perfectly adherent to the zoha pellucida. 

 v. Beneden also recommends the liquid of Kleinenberg. 

 Henneguy writes that he frequently employs it for embryonic 

 areas and embryos of various ages, always with excellent 

 results. Fol's modification of the liquid of Flemming, and 

 Hanvier and Vignal's osmic acid and alcohol mixture ( 28), 

 also give excellent results. For staining, Henneguy recom- 

 mends borax-carmine or Delafield's hgematoxylin for small 

 embryos; for large ones, Henneguy's acetic acid alum-car- 

 mine is the only reagent that will give a good stain in the 

 mass. 



For sections, pure paraffin. Cut in series and mount in 

 balsam. 



PIERSOL (Zeit.f. wiss. Zool, xlvii, 2, 1888, p. 155) has been 



