320 BULLETIN OF THE 



vations on Nephelis. In Brachionus (p. 247) the radial figures appear 

 suddenly in the yolk at two opposite points of the nucleus, and at each 

 of these places is formed a re-entrant surface. These surfaces advance 

 till they meet, and thus seem to cause the disappearance of the nucleus. 

 The process, however, as acetic acid preparations show, is only a nuclear 

 metamorphosis, which advances from the points mentioned. The division 

 of the nuclear plate and the migration of its halves was observed in No- 

 tommata. In the two genera mentioned, only a single new nucleus is 

 formed in each new segment. Why Biitschli cites in this connection 

 Flemming's ('75, Taf. III. Fig. 2) figure of Anodonta as making probable 

 the ultimate discovery of a cell plate in the Rotifera, I cannot conjecture, 

 unless he made the mistake of supposing that the figure above cited was 

 that of a rotifer's egg. Biitschli remarks, with reason, that he has never, 

 even in the rotifers, seen the new nuclei in the centre of the stellate 

 figure, as Flemming has drawn them in the case in question. 



In a pseudovum of Aphis, Biitschli also once saw two small nuclei joined 

 by delicate filaments. The nuclei of the blastoderm, he therefore con- 

 cludes, arise by successive divisions of a single nucleus (p. 249). More- 

 over, the blastoderm cells of a butterfly and of Musca vomitoria (p. 261) 

 were demonstrated to present the striate spindle-shaped differentiation 

 of the nucleus. In the former the equatorial nuclear plate was clearly 

 seen ; in the latter, only irregularly distributed local thickenings of the 

 spindle fibres. In Musca the radiation of the protoplasm about the ends 

 of the spindle was very distinct. 



The second section of the fourth chapter of Biitschli's paper (pp. 394- 

 419) is devoted to a general consideration of nuclear and cell division. 

 The author considers, with Strasburger, that the increase of nuclei by 

 means of a metamorphosis into a fibrous spindle-shaped structure is to 

 be regarded as the original and typical method. But there exists with- 

 out doubt another mode of nuclear division which greatly differs from 

 this, or at least may be referred back to it only by assuming very radi- 

 cal modifications (e. g. blood-disks of Rana, etc.). Supported by the 

 existence of a very delicate, yet exceedingly distinct membrane, envelop- 

 ing the nuclear spindle of the infusorian "nucleoli," the author assumes 

 a similar membrane for all other nuclear spindles, and as evidence of his 

 correctness calls attention to the distinct contour which was seen by 

 Strasburger to surround the nuclear plate of certain vegetable cells when 

 the plate was viewed en face. The indistinctness of the nucleus in the 

 living egg when it is undergoing its spindle metamorphosis the author 

 explains as due to three causes : (1.) the disappearance of the so-called 



