182 THOMAS H. 1311YCE. 



acid and the sublimate mixtures^ aud by other stains besides 

 the iron hasmatoxj'lin, though the greatest vividness of 

 differentiation has been obtained by a combination of Her- 

 mann's or Flemming's fluid with iron htematoxylin, and, 

 second, that the proof that I am dealing with realities aud 

 not illusions is to be found in the fact that the appearances 

 described for the chromosomes represent a complete and 

 unbroken series of the steps or stages of a process that cau 

 be explained only by reference to the completed story. 



The drawings were made by aid of the Abbe drawing 

 appai'atus of Zeiss, the finer detail being filled in free- 

 hand. The combination used was in every case Zeiss 

 2 mm. 1"40 numerical aperture, apochromatic objective, 

 with either eight or twelve compensating eye-piece. The 

 illuminating apparatus employed was a Zeiss 1 mm. 

 numerical aperture, achromatic condenser. The sections 

 were cut in paraffin, and were of varying thickness. The 

 object in most cases being to obtain the masses of chromatin 

 entire, comparatively thick sections were taken, six to seven 

 microns. Thinner sections down to three microns were 

 employed to determine certain points regarding the achro- 

 matic structures. 



In dealing with the subject 1 shall first describe the 

 changes in the ovum leading up to the disappearance of the 

 germinal vesicle, and after that treat in separate sections of the 

 behaviour of the achromatic and of the chromatic structures. 



My earliest preparations are from the growth period. Out 

 of a large number of young oocytes of the first order I have 

 only seen two or three in mitotic division, and these only in 

 the spireme stage, so that I cannot speak as to the number 

 of chromosomes in these divisions. The young ovum shows 

 a delicate reticular protoplasmic structure (fig. 1). The 

 nucleus is already largo and vesicular, wnth a distinct 

 nuclear membrane, and a deeply staining eccentric nucleolus. 

 This being intensely black, contrasts strongly with tlie 

 granular and iri-egular nuclear network, which refuses to 

 take on the chromatin stain, aud remains pink in prepara- 



