FRANZ SCHRADER. 



plain that condensation of chromosomes progresses regardless of 

 the phase of an apposed nucleus, and that therefore the period of 

 suspension of activities occurs when the chromosomes have been 

 fully evolved. 



Whether complete fusion of such nuclei is ever brought about 

 before the condensation of chromosomes cannot be answered 

 with certainty. A cytological demonstration would be next to 

 impossible if the act is a very short one say like the fusion of two 

 soap bubbles to make a single larger one. That I have no stages 

 showing such an act is therefore not complete proof that it does 

 not occur. Nevertheless the normal course consists of a condensa- 

 tion of the chromosomes entirely independent of any other 

 nucleus, and the fusion occurs only when the nuclear walls break 

 down and permit an intermingling of all the chromosomes. 



It is owing to the conditions brought out in the preceding 

 paragraphs that a very good cytological demonstration of the act 

 of fusing can be given. In Fig. 10 are shown three nuclei in 

 apposition, and in the light of the numerical data they may 

 safely be assumed to represent one polar nucleus derivative and 

 two cleavage nuclei. Without the numerical data however, no 

 such assumption would be justified. Fig. n on the other hand 

 furnishes strikingly independent proof. Here there are 20 

 chromosomes almost fully condensed, and these show a slight 

 trace of being arranged in two groups of 10 each. But in addition 

 there are 15 chromosomes still in a more threadlike stage, and 

 evidently at an earlier phase of condensation. The figure evident- 

 ly represents a case in which the nuclei when coming into apposi- 

 tion were at different phases. The conclusion seems inescapable 

 that here is represented the fusion of a polar nucleus derivative 

 with two cleavage cells. 



Spindles formed in the first division of these combination or 

 fusion nuclei are apparently perfectly normal. Multipolar spin- 

 dles are indeed encountered but little if any more frequently at 

 this time than they are in the normal tissue of many animals. I 

 am entirely at a loss to explain how the mitotic mechanism of two 

 or even three combining nuclei is adjusted to the process of 

 fusion. Certainly all the involved nuclei are capable of dividing 

 perfectly independently. Bowen ('22) has recently pointed out a 



