42 



in the form of spherules and that previously imbibed by the plastin is 

 all at approximately the same stage of elaboration or chemical com- 

 position. The living material shows the nucleolus with a vacuolated 

 structure because of the difference in refractive index between the more 

 fluid chromatin of the spherules and the more viscid or semi-solid 

 constituency of the plastin combined with the imbibed chromatin. The 

 vacuoles seen in the nucleoli of stained material at certain stages are 

 due to the fact that the highly fluid chromatin which has entered the 

 ground substance in the form of spherules has been imbibed by the 

 plastin, leaving behind the empty spherules as vacuoles in the plastin, 

 and which appear stained according as the underlying plastin is stained. 



In favorable cases where the chromosome group is not too com- 

 pact, I have been able to count from 14 to 18 bilobed chromatic 

 bodies. Comparison with a section through a chromosome complex 

 from the central pole of the first maturation spindle shows such a 

 close similarity of form between the two groups as to amount virtually 

 to an identity. The only difference is one of size, this being in favor 

 of the chromosomes from the polar spindle. There remains no doubt 

 that this group of bilobed bodies are the chromosomes which have 

 persisted with identity unimpaired through the entire growth period. 

 When maturation is immaneut, the chromosome group is invariably in 

 a position next the nuclear wall at the point where the single aster 

 arises and where rupture of the wall subsequently occurs. 



Contrary to Mathews' ('95) observation that the centrosomes 

 arise from within the nucleus, rupturing the wall as they pass out, 

 I have seen the single aster form, divide, and its products separate 

 outside of the nucleus while the nuclear wall was still intact. I believe 

 that the centrosomes arise from the cytoplasm as also reported by 

 Griffin ('99) in the case of Thallasema and Zirphaea, and by various 

 other investigators in other forms. My observations of course do not 

 exclude the possibihty of their origin from the outer layer of the 

 nuclear wall. 



Rupture of the nuclear wall at maturation seems to be caused 

 by pressure exerted by the astral rays of the polar spindle combined 

 probably with a solvent influence of some sort. Ordinarily the nucleolus 

 is also in position near the point where the astral rays enter the nucleus. 

 Not infrequently, however, it is located at the opposite pole. This is 

 strong evidence that the chromosomes do not come from the nucleolus, 

 for chromosomes are frequently already within the polar spindle when 

 the nucleolus is just beginning to fragment at the other pole. A single 

 specimen adds still further proof that the chromosomes do not arise 



