THE ARCHOPLASMIC STRUCTURES 325 



Other cases a sphere closely simulating an attraction- sphere may 

 arise in the cytoplasm without apparent relation to the centrosomes 

 or to the preceding aster, e.g. the yolk-nucleus or the sphere from 

 which the acrosome arises in mammalian spermatogenesis.^ To call 

 such structures "attraction-spheres" or " archoplasm-masses " is to 

 beg an important question ; and in all such doubtful cases the simple 

 word sphere should be used.^ In case of the aster itself we may, for 

 descriptive purposes, employ Strasburger's convenient and non-com- 

 mittal term centvospherc, to designate in a somewhat vague and general 

 way the central mass of the aster surrounding the centrosome, leaving 

 its exact relation to Van Beneden's attraction-sphere to be determined 

 in each individual case. Where the centrosphere shows two concen- 

 tric zones (medullary and cortical), they may be well designated with 

 Ziegler as entospherc (" centrosome" of Boveri) and eetosphere. 



As regards the structure of the centrosphere, two well-marked types 

 have been described. In one of these, described by Van Beneden in 

 Ascaris, by Heidenhain in leucocytes, by Driiner and Braus in divid- 

 ing cells of Amphibia, and by Francotte, Van der Stricht, Lillie, Kos- 

 tanecki, and others, in various segmenting eggs, the centrosphere has 

 a radiate structure, being traversed by rays which stretch between the 

 centrosome and the peripheral microsome-circle (Fig. 152, D, E, F), 

 when the latter exists. In the other form, described by Vejdovsky in 

 the eggs of Rhynchelniis, by Solger and Zimmermann in pigment-cells, 

 by myself in Nereis, by Rlickert in Cyelops, by Mead in Clitjetopterns, 

 Griffin in Tkalassetna, Coe in Cerebratulus, Gardiner in Polychoerus, 

 and many others, the centrosphere has a non-radial reticular or vesicu- 

 lar structure, in which the centrosomes lie (Figs. 152, H, 155). Kos- 

 tanecki and others have endeavoured to show that such structures are 

 artifacts, insisting that in perfectly fixed material the astral rays always 

 traverse the centrosphere to the centrosome. This interpretation is, 

 however, contradicted by the fact that the new asters developing in 

 the centrospheres during the anaphases and telophases of such forms 

 as Thalasseuia or Cerebratulus (Figs. 99, 155) show perfect fixation of 

 the rays. The reticular centrosphere almost certainly arises as a nor- 

 mal differentiation of the interior of the aster, which, as Griffin ('96) 

 has suggested, probably marks the beginning of the degeneration of 

 the whole astral apparatus, to make way for the newly developing 

 system. 



The radial centrosphere is in Ascaris divided into cortical and medul- 

 lary zones, as already described (p. 310), the aster being bounded by 

 a distinct circle of microsomes. The true interpretation of these zones 

 was given through Heidenhain's beautiful studies on the asters in leu- 

 cocytes, and the still more thorough later work of Driiner on the sper- 



1 Cf. p. 170. , '^ CJ. Lenhossek, '98. 



