24O O. C. GLASER. 



velopmental period considered have four times as many. As the 

 period during which this increase chiefly occurs exhibited but 

 one mitosis among 1,751 nuclei, the conclusion is practically 

 forced on one that amitosis is the method of cell multiplication 

 that obtains in the entoderm. 



This conclusion however must be critically tested. Is there 

 any possibility that after all one mitosis among 1,751 nuclei is 

 enough to account for the facts of growth ? This question can, 

 I think, be definitely answered in the negative. 



The time taken by a larva in stage III. to change into stage 

 IV. is 13 days ('05). During this period, according to the 

 determinations, the number of cells in the transverse planes under 

 consideration increases from 20 to 93, an addition of 73 cells. 

 Let us assume for the sake of argument that a complete mitosis, 

 beginning with a resting mother nucleus and ending with two 

 resting daughter nuclei can be accomplished in one minute. As 

 i- per cent, of the nuclei are dividing mitotically, it follows that 

 in one minute .0005 mitosis occur. In 2,000 minutes therefore 

 one complete mitosis would take place. Since 2,000 minutes 

 equal 33 hours, it follows that once in this number of hours an 

 entoderm cell would divide. Now the developmental period 

 under examination endures 13 days, or 312 hours. If therefore 

 one division takes place every 33 hours it follows that 9 such 

 cleavages would occur in the 13 days. As the larva has " 20 " 

 cells to begin with, the first division would raise this number to 

 21; the second to 22; and the ninth to 29. Thus if mitosis 

 occurs at the determined rate of ^ per cent., and at the assumed 

 speed, 9 new cells would have been produced. The actual counts 

 show that 73 cells are added. Even if we double the speed and 

 assume that a mitosis can be completed in 30 seconds there would 

 still be a disparity of 5 5 cells. If this reasoning is correct, mitosis 

 occurring with the frequency actually determined, is totally insuffi- 

 cient to account for the observed facts of growth. 



One chance however remains. It is possible that my deter- 

 minations of the frequency of mitosis during this developmental 

 period are misleading ; that I missed the epidemics of division, 

 three of which would more than explain the facts, for if all of the 

 20 cells in stage III. were to divide at once the number would 



