326 BULLETIN OF THE 



in Serpula immediately preceding and accompanying segmentation. (See 

 p. 428.) 



After alluding many times to the priority of his own discoveries in 

 this field of research, Fol (76") communicates important new consider- 

 ations resulting from his studies on Heteropods, the sea-urchin, and 

 Sagitta. 



The centres of attraction appear before each segmentation at opposite 

 poles of the nucleus, which is still absolutely intact, and seem to be local 

 fusions of the substance of the nucleus [not quite "absolutely intact"?] 

 with the vitelline protoplasm, or perhaps an irruption of protoplasm into 

 the more fluid interior of the nucleus. 



The difference in the appearance of the intranuclear (spindle fibres) 

 and the extrauuclear filaments results from the former being immersed 

 in a medium almost liquid and much less refringent than the protoplasm 

 of the filaments, while the latter are bathed in protoplasm, and for that 

 reason ought not to be so easily distinguishable. The difference between 

 these filaments is therefore only apparent and depends on the properties 

 of the substances surrounding them. 



If the varicosities discovered by Biitschli appeared only upon the 

 intranuclear filaments, they would, in Fol's opinion, establish a remark- 

 able diff'erence between the two kinds. But that is not the case. 

 In the eggs of Geryonia and the sea-urchin varicosities are to be found 

 upon the extrauuclear filaments, which have hitherto escaped all observ- 

 ers. These enlargements are more elongated and less regular than those 

 of the interior of the nucleus, but they are, after all, indubitable vari- 

 cosities, which migrate like the others, and slowly become fused with the 

 central mass of protoplasm. This mass is, therefore, neither in its mode 

 of origin nor growth exclusively a derivative from the substance of the 

 old nucleus ; it is the result of a fusion of a part of this substance with 

 a part of the vitelline protoplasm. 



As to the relation of these central masses to the new nuclei, the author 

 says he has often observed that, after having absorbed the greater part 

 of the radial filaments and their thickenings, they exhibit spots which 

 are clearer and probably more liquid than the rest of the mass, and which 

 have on this account been styled vacuoles. The new nucleus is the re- 

 sult of the fusion of these vacuoles. That which remains of the central 

 mass constitutes the envelope of the nucleus. Often, but not always, a 

 vacuole arises outside the central mass, on the side toward the old nu- 

 cleus. This shows that the liquid of the nucleus has the same double 

 origin as the masses themselves. The new nuclei result from a partial 



