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be traced through the spheres to the centrosomes (Dia. B, 1, 2, 3); 

 in the anaphase and telophase the rays can be traced only to the 

 spheres, not into them, and the interior of the spheres becomes alveo- 

 lar (Dia. B, 4, 5); finally during the rest the spheres become finely 

 granular (Dia. B, 6). At all times the spheres show great affinity 

 for plasma stains and are sharply difierentiated from the surrounding 

 cytoplasm; even after the new centrosomes and central spindles have 

 migrated out of the spheres (Dia. B, 7), the latter remain for a long 

 time as irregular masses of deeply staining granules. These remnants 

 of the spheres persist through one or two cell generations and in 

 division are differentially distributed, always going into one daughter 

 cell and not into the other, as I have described elesewhere ^). 



The more important characteristics of the spheres may be summed 

 up as follows: 



1) They are composed of a specific substance, temporarily dif- 

 ferentiated from other cell constituents. 



2) This substance is not self propagating but arises anew in each 

 cell generation being composed of nuclear sap and of dissolved oxy- 

 chromatin from the nucleus, and of hyaloplasm from the cell body. 



3) This substance forms a large part of the spindle and aster 

 and at the close of karyokinesis it is collected into large sphere sur- 

 rounding the centrosome. 



4) When in the prophase of the next division, the new centro- 

 somes and central spindle move out of the sphere, the latter becomes 

 irregular in shape and, through it may persist for a long time, it 

 ultimately disintegrates into coarse granules which are scattered in 

 the cytoplasm immediately under the cell membrane. 



The points of resemblance and difference between this substance 

 and the archoplasm of Boveri will be apparent without further com- 

 ment ; its resemblance to the idiozome of Meves is so marked that I 

 cannot doubt that the two are homologous. 



1) CoNKLiN, The Asters in Fertilization and Cleavage. Science, 

 March, 1898. — Protoplasmic Movement as a Factor of Differentiation. 

 Woods Holl Lectures, 1899. 



