460 WILSON. [Vol. XI. 



in some cases the entire centrosome, in other cases only a 

 portion of it.)^ 



A. Observations. — A few moments after the entrance of the 

 sperm-head the middle-piece may in favorable preparations be 

 seen as a definite rounded mass lying at the base of the conical 

 sperm-nucleus, though sometimes its boundary is lost in the 

 surrounding protoplasm. I cannot find in this mass anything 

 to be identified with a centriole. It consists of a uniform 

 finely granular or nearly homogeneous substance which, like the 

 middle-piece of the free spermatozoon, stains a clear pale blue 

 in iron-haematoxylin, but after double staining with hsematoxy- 

 lin and a red plasma stain like Congo red is purplish or reddish. 

 About the middle-piece as a central mass, the astral rays are 

 formed, and their thickened bases are directly continuous with 

 its substance (Text-fig. I). 



The central mass rapidly increases in size as the aster moves 

 towards the egg-nucleus, and upon coming in contact with the 

 latter extends around one side of it like a cap. It then draws 

 apart into two rounded masses which place themselves at oppo- 

 site poles of the cleavage-nucleus, each surrounded by long 

 astral rays which soon afterwards shorten up and become more 

 granular, as described at p. 452. 



Up to this period the central mass retains its original struc- 

 ture, and shows no trace of differentiation. Now, however, a 

 change, both morphological and chemical, takes place in its 

 substance. A small, ill-defined mass appears in the center of 

 each aster, in the immediate neighborhood of the nuclear mem- 

 brane, composed of a substance which stains but slightly in the 

 haematoxylin but is colored bright red by Congo red. In the 

 interior of this mass appear one or two extremely minute 

 granules (centrioles), which stain deep blue in the haematoxylin 

 (Text-fig. IV). The aster is at this period closely similar to 

 those of Ascaris at certain periods, as figured by Boveri, and 

 the red mass with its central group of granules corresponds 



^ In my former paper (Journal of Morphology, X, i, 1S95) ^ have termed 

 the centrosphere an " attraction-sphere " or " archoplasm-sphere." In view, how- 

 ever, of Boveri's identification of this mass as the centrosome, this terminology 

 becomes so misleading that it will be abandoned in favor of the above. 



