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ORIGIN OF MYCETOCYTES IN PSEUDOCOCCUS. 28 1 



her of chromosomes is ten, all being alike in size and shape (Figs. 

 1-3). Five tetrads are formed in the maturing egg, and the egg 

 nucleus undergoes a reduction and an equation division. The 

 order in which these two divisions occur cannot be ascertained. 

 The first division results in two daughter groups each consisting 

 of five dyads. One of these groups of course represents the first 

 polar body. It is not extruded but remains in an inactive state 

 at the periphery. The other group of dyads undergoes the second 

 maturation division, the results of which are two groups, each 

 containing five unit chromosomes or monads. One of these last 

 two groups remains at the periphery, constituting the second 

 polar body. The other sinks into the egg and there combines 

 with the male pronucleus. 



The five dyads of the first polar body now break up into their 

 unit elements, ten in number, and then enter the resting condi- 

 tion. The five monads of the second polar body also become 

 diffuse. The two polar bodies then approach until in touch 

 with each other. Fusion may then actually occur and I have 

 described such a case in my previous paper ('23). In other cases 

 however fusion is delayed until the chromosomes of each have 

 been almost completely reformed and the nuclear walls begin to 

 break down. The chromosomes then intermingle to form a 

 single group, and this of course contains 15 chromsomes. With 

 this act of combination the polar nucleus becomes established 

 (Fig. 4)- 



The polar nucleus undergoes two or three divisions which 

 appear normal in every respect (Fig. 4 to 7). Following the last 

 of these divisions, irregularities occur, and in the course of these 

 the chromosomes are greatly increased in number and the size 

 of the cells is enlarged. These phenomena occur in every egg and 

 the resultant cells I have called giant cells. The giant cells once 

 established, undergo some apparently normal divisions and 

 then become separated from the periphery and migrate a con- 

 siderable distance through the egg to the symbionts. With these 

 they enter into association and thus form the mycetocytes, which 

 in this manner are formed anew in every embryo. 



Although this account portrays the general course of events, 

 it leaves unexplained the exact nature of the irregularities which 



