(9) 



stance is secreted, in which, as it hardens, the foreign 

 particles become firmly embedded. After the new shell is 

 formed, the parent protoplast is partially retracted into 

 the old shell, the nucleus divides, and ultimately the pro- 

 toplast pulls apart into two organisms, and the parent and 

 its offspring separate. 



The regular mitotic division of the nucleus during this 

 process has been described and figured by Schaudinn (1903, 

 1911). Unfortunately, although a c?iromidial ooay is present. 

 ( see Figure 2), no account of its behavior during cell 

 division has been published. 



The new shell, wher; first formed, is almost white, in 

 striking contrast to the dark brown color of old shells. 

 The darker coloration is taken on gradually, first appearing 

 as a faint yellowish tinge, which slowly deepens to brown. 

 Even when four or five individuals have com.e from one in the 

 course of a week or so, their relative ages, and therefore 

 their parentage, is unmistakably indicated Vy their color. 

 In practise, however, it was only very rarely that either 

 of the two products of a division had time to uivide again 

 before they were separated. At ordinary laboratory tempera- 

 tures, dioring the cooler months, Centropyxis aivides about 

 twice a week, at most. Inspection of tlie cultures at inter- 

 vals of two or even three days was ordinarily sufficient, to 

 insure -the isolation of parent and progeny before either had 

 divided a second time. 



In closing this brief ucscripoion ui the organism used 

 in this experiment, I wish again to emphasize the fact that 



