464 WESLEY R. COE, 



gradually become exactly similar to the granules of the centrosphere 

 into which they eventually merge. As the centrosphere enlarges the 

 aster-fibres disappear in its interior at a somewhat corresponding rate, 

 and at the same time we find that the minute granules of the centro- 

 sphere are being arranged in a sort of reticulum, the meshes of which 

 only gradually become evident. It is only in the cleavage-asters that 

 the centrosphere develops sufficiently to show a reticular (or vesicular) 

 arrangement of its substance. In its maximum development the aster- 

 fibres end on its periphery, instead of penetrating towards the interior. 

 During all this time the centrosomes which divided at a very early 

 period, have scarcely increased in size, and each has been continually 

 surrounded by a finely granular substance more homogeneous than 

 that of the large centrosphere. This delicate sheath, although situated 

 within the substance of the centrosphere, can hardly be considered 

 other than as the "Anlage" of the centrosphere of the second cleavage- 

 spindle. Objections to considering this delicate sheath as a "centrosome" 

 rather than a centrosphere arise from the fact that it is seen to be 

 directly continuous with the developing aster-fibres; that it does not 

 stain black with Bordeaux and iron-haematoxylin ; that centrosomes 

 may be found (as in the outer pole of the polar-spindles and in the 

 degenerating asters of the sperm-nucleus) which have no such sheath 

 of protoplasm ; and, finally, that it is present in such an exceedingly 

 varying quantity. As Griffin remarks for Thalassema, that the body 

 here called the centrosome is the actual centrosome is shown by the 

 fact that it multiplies by division and persists from one cell-generation 

 to another, while the centrosphere (corresponding to the „Centrosom" 

 of BovERi) is merely a transient structure similar to the aster-fibres 

 and disappears completely previous to the second cleavage. 



A most interesting example of the persistence of the centrosomes 

 and the transient nature of the centrospheres is shown in Fig. 39, 

 As will be seen at a glance, there has here been a serious disturbance 

 either of the cell-substance or of the cleavage-spindle. This disturb- 

 ance evidently took place after the complete formation of the spindle 

 and the division of the chromosomes , for the greater portion of the 

 spindle is perfectly normal. Peripherally, however, the cell-substance 

 seems to have revolved in a left-handed manner so that the aster- 

 fibres and the ends of the spindle have been bent a right angles to 

 the main axis of the spindle. The centrospheres have disappeared 

 entirely, leaving the pair of centrosomes in each pole lying free among 

 the aster-fibres, and somewhat farther removed from the ends of the 



