DEVELOPMENT OF DISTIOHOPOEA VIOLAOEA. 65 



bryonic development a multinucleated plasmodium without 

 any definite cell walls or cell areas. 



There can be little doubt, I think, that in all holoblastic eggs, 

 such as those of Echinoderms, worms, Amphioxus, &c., the first 

 segmentation is accompanied by typical karyokinetic division 

 of the nucleus. 



We may go further than this, and say that in many mero- 

 blastic eggs the first divison of the oosperm nucleus is also an 

 indirect one. Vialleton (57) and Watase (59) have observed 

 this division in the egg of Cephalopoda, and Oppel (45) has 

 observed it in the egg of the lizard, Anguis fragilis. But 

 in both these cases the segmentation furrows occur regularly 

 and in sequence from the commencement of development, and 

 ■we have, consequently, evidence that the same forces are at 

 work in the protoplasm as those which produce the more or 

 less complete blastomeres of holoblastic eggs. Even in those 

 eggs of insects in which the nuclei are known to divide by 

 karyokinesis there is evidence of the drawing together of the 

 protoplasm along certain lines of force in the " plasmatische 

 Strahlungen" of Henking, which surround the nuclei. 



But if there is any truth in the view that I have here put 

 forward, that karyokinesis is primarily due to the forces which 

 bring about cell division, and that in those cases in which cells 

 or cell areas are not formed the nucleus may fragment or 

 divide directly in some other way, then we should expect to 

 find some further evidence of fragmentation of the nucleus in 

 other tissues. There is ample evidence of this in other tissues. 



In the formation of the spores in Protozoa the nucleus of 

 the parent cell often divides long before there is any division 

 of the cell protoplasm, and in nearly all such cases division of 

 the nucleus is direct. In some cases the nucleus disappears, 

 and it is probable, as in the case of the oosperm nucleus 

 quoted above, that this may be due to the extremely fine 

 division of the chromosomes and fragmentation. 



I will give just a few examples to illustrate these points. 



Wolters (64), in describing the conjugation of Monocystis 

 magna and agilis, says, " Kurz nach erfolgter Encystirung 



