THE CENTROSOME 22 J 



that both these structures are persistent and that division of the sphere 

 is preceded by division of the granule (Fig. 107). The central granule 

 is exactly like the simple centrosome of the sperm-aster as described 

 above, but we do not yet know with certainty the genesis of the 

 sphere surrounding it, and hence cannot state whether this is part 

 of the centrosome proper or a part of the centrosphere surrounding 

 it. The former view is adopted by Boveri, who suggests the word 

 " centriole " for the central granule; and, according to his observa- 

 tions on Ascaris and on sea-urchins, the simple centrosome of the 

 original sperm-aster enlarges to form the sphere, while the centriole 

 afterwards appears within it. In the case of T/ialassenia, however, 

 Grififin's observations leave no doubt that the central granule per- 

 sists in its original form from its first appearance in the sperm-aster 

 through every stage of the cleavage-amphiaster, dividing during the 

 early anaphase in each aster and giving rise to the centrosomes of 

 the daughter-asters in which it again appears as a simple granule at 

 the focus of the rays without a trace of surrounding envelopes 

 (Fig. 73). In the cleavage-amphiaster it is surrounded by a some- 

 what vague, rounded mass (apparently representing the entire " cen- 

 trosome " of Boveri and Brauer), which in turn lies in a reticulated 

 centrosphere, from which the rays radiate. Both these structures 

 disappear during the late anaphase, leaving only the central granule. 

 Here, therefore, the true centrosome certainly corresponds to the 

 central granule or centriole ; and all the surrounding structures be- 

 long to the centrosphere. 



As soon as we look further we find apparent departures from this 

 simple type of centrosome. In leucocytes Heidenhain finds at the 

 centre of the centrosphere not one or two, but always three, and some- 

 times four, granules, which he conceives as centrosomes forming a 

 central group or microcentrum. In the giant-cells of bone-marrow 

 the central group consists of a very large number (a hundred or 

 more) of such granules, each of which is again conceived as a 

 "centrosome " (Fig. \\,D). In the sea-urchin {Echinus) Boveri states 

 that the original simple centrosome of the sperm-aster enlarges 

 greatly to form a relatively large, well-defined sphere in which 

 appear numerous granules (centrioles), which he would compare 

 individually with the elements of Heidenhain's "central group." 

 I have given a somewhat similar account of the facts in Toxopjicn- 

 stcs, describing the centrosphere as a reticulated mass derived from 

 an original granule or centrosome at the focus of the rays,^ and many 



1 Professor Boveri informs me tliat I was in error in attributing to him the view that the 

 entire central mass of the aster — i.e. the centrosphere — here represents the centrosome. 

 The large spherical centrosome of Echinus is surrounded by a clear area which he regard? 

 as the centrosphere. 



