276 WATASE. [Vol. IV. 



point as to the origin and movement of tlie arclioplasm itself. 

 But as a matter of fact, we know as yet very little in regard to 

 the origin of the archoplasm, which has sometimes a definite 

 body in its centre — the centrosome. A great authority like 

 van Beneden looks upon it as a permanent organ of the cell, 

 equal in value to the nucleus itself ; but the whole question of 

 its origin and its apparent homologues, which pass by different 

 names in different cells, is too complicated and obscure to be 

 discussed in this place. 



The later history of the archoplasm is, however, better known. 

 When we examine a cell at the close of caryokinetic division, 

 we see a small nucleus with the archoplasmic sphere at one side 

 of it, appearing somewhat like a satellite of a planet. This 

 small nucleus is one of the daughter nuclei of the previous gen- 

 eration, and is destined to become the mother nucleus of the 

 next. Just as new nuclei arise by the division of the old one, 

 so the new archoplasmic spheres also arise by the division of 

 the previous one. In the Cephalopod blastoderm the division 

 of the mother archoplasmic sphere into two daughter spheres 

 could be observed with sufficient clearness. In Ascaris, its 

 division has been most carefully studied by several investiga- 

 tors. At first the two daughter spheres lie in close opposition ; 

 later, they separate more and more widely. As each sphere has 

 a system of radiating filaments, there is formed a little spindle 

 where they come into contact. This spindle lies outside of the 

 nucleus, and has nothing to do with the larger one which has 

 been described already. The daughter archoplasmic spheres 

 migrate further apart, and finally settle themselves on the 

 opposite sides of the nucleus. Their effect on the latter is soon 

 seen. That surface of the nucleus upon which the archoplasm 

 rests soon shows signs of flattening, as was shown in Fig. VII. 

 This polar flattening of the nucleus has been interpreted as due 

 to the pressure exerted by the growing archoplasmic filaments. 

 The growth of the filaments continues, and the effects it pro- 

 duces upon the nucleus, in the arrangement and distribution of 

 the chromosomes, have already been described. Compare in 

 this connection the series of stages shown in Figs. VII, VIII, 

 IX, and V. 



The above is a brief sketch of the mechanics of nuclear 

 division, as I interpret them from the study of Cephalopod 



