364 Dr. II. E. Zieg'Icr on Amitofic Nuclear Division 



division." In my previous paper I dilated upon the fact that 

 *' in cases of a widely different character we find peculiar 

 forms of nuclei, which we may class together with the nuclei 

 of the periblast of Teleosteans, and that tiiese phenomena 

 constitute an important chapter for the natural history of the 

 cell-nucleus in general." " It would seem fitting were we 

 to use the ex])ression fragmentation in the animal kingdom 

 (and, indeed, in the first place only for the ^letazoa) for those 

 mor[)hologically and physiologically associated cases which 

 are characterized as follows. The nuclei are considerably 

 larger than the ordinary nuclei in the same animal, and 

 exhibit an abnormal poverty, or an abnormal distribution, of 

 chromatin. The nuclei multi})]y by direct nuclear division j 

 it often happens that the division is not carried as far as the 

 separation of the segments, so that the nuclei show bud-like 

 processes and irregular prolongations, or appear divided by 

 constrictions. Fragmentation occurs in cells which no longer 

 undergo division, or in masses of protoplasm which have 

 arisen through incomplete cell-division {i. e. through nuclear 

 division without concomitant division of the cell). The 

 appearance of fragmentation is connected with the fact that 

 the cell has become specialized, has adapted itself to a definite 

 physiological function, that, for instance, it is harbouring and 

 assimilating food-yolk, is performing some process of secre- 

 tion or absorption, &c. 1 he nuclei have degenerated, in so 

 far as the cell is no longer capable of division, and conse- 

 quently can no longer morphologically take part in the further 

 building-up of the embryo or in processes of regeneration; it' 

 in this sense we designate the nuclei as degenerate, this does 

 not preclude them from performing their physiological func- 

 tion for a longer or shorter time. There are simpler modes 

 of degeneration which lead to speedy destruction ; fragmen- 

 tation only occurs when the nuclei first undertake a specialized 

 function and then jx'rish." 



" Within the blastoderm, scattered about in the yolk, are found, a.-* is 

 well known, in the Muscidje, as well as in all Insects liitherto investigated, 

 cells, or at least nuclei, whicli we consequently very frequently term 

 yolk-cells (" Vitellophaj^a, ' according to Aussbaum). Now as regards 

 the share which these nuich-di.-cu.-sed cells take in tlie building-up of 

 tiie embryo, at present far the most generally accpted view is that thev 

 merely assist in the a.~.-iinilatioii of the yolk, lUid that, althoiigli they and 

 the cells of the blastoderm have a common origin, the former elements 

 take no special part in the foimaliou of tissues, and are not lo be included 

 in the category of the true germinal layers.'" Tlie vitellophag-a of the 

 Muscida' are nuclei witliout a plasma-en velcpe. and appear " as generallv 

 very irregularly detined or ama'boid structures of relatively gigantic 

 eize." 



