MATURATION OF OVUM IN ECHINUS K80ULENTUS. 181 



the sublimate material the centrosome gave quite a different 

 picture, as will be seen in the sequel. 



Staining. — Osmic acid preparations being proverbially 

 refractory to most staining reagents I have confined myself 

 almost entirely to Heidenhain's iron hajmatoxylin method, 

 but have used by way of control other staius. To facilitate 

 staining I have always allowed my preparations to stand for 

 some time in old turpentine to remove the osmic acid. The 

 best results were obtained by iron htematoxylin alone, the 

 picture presenting the vivid black chromosomes on a blue- 

 grey field. Heidenhain's preliminary stain with Bordeaux 

 red rather confuses the picture of the chromatin, and the 

 only other contrast stain used was a very weak coloration 

 by alcoholic solution of fuchsin S. 



It is necessary here to refer to the recent criticism by 

 Boveri (1901) of the iron hsematoxylin stain. He shows, as 

 every one knows who has used the method, that different 

 degrees of washing out yield different results, and refers to 

 the fact that structures may appear which owe their existence 

 to a purely mechanical cause and not to any difference in 

 chemical composition. Thus a part which is not readily 

 accessible, on account of its position, to the differentiating 

 fluid retaius the stain while the parts in the neighbourhood 

 are decolourised ; further, the fluid having a concentric 

 effect in washing out, the superficial parts are decolourised 

 while the central parts retain Lhe black stain. Thus he 

 explains the different accounts given of the structure of the 

 centrosome, and points out that by strong extraction of the 

 colour even the chromosomes may be apparently diminished 

 in size owing to their peripheral parts being decolourised. 

 This is weighty criticism in view of a number of the 

 appearances I shall have to describe, for he combats the 

 generally accepted view that the true appearances are 

 obtained by strong washing out, and believes that in regard 

 to the centrosouies the opposite is true. As to the chromo- 

 somes I may forestall criticism of my results by stating, first, 

 that I have obtained similar appeai'ances both with the osmic 



