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William S. Marshall and Paul H. Dernehl, 



number, six, of nuclei within tbe egg; these are not central in their 

 position, but all lie nearer tbe anterior tban tbe posterior pole, 

 confined to the anterior half of tbe egg. A similar occurrence, as 

 to position, of tbe few nuclei at first found witbin tbe egg, bas been 

 observed for a number of otber insects by Weismann (59) in Chiro- 

 nomus, Kowalevsky (31), Grassi (19) and Dickel (14) in Apis, 

 Bobretzky (3), in Pieris, Heider (22) in Hydrophilus, and Carriere 

 and Bürger (11) in Ghalicodoma. What relation tbis localization of 

 tbe first few nuclei bas to tbe position of the first segmentation 

 nucleus within tbe egg we are unable to say; whether the latter 

 originally occupied the same relative position or wandered tbere 

 from some otber part of tbe egg. Otber than their being in a certain 

 part of tbe egg there is no arrangement of these first nuclei relative to 

 each otber or any axis of the egg itself. Whenever, during these early 

 stages, any nuclear divisions were noticed, they were always mitotic. 



The nuclei divide, increasing in number, all remainiDg for some 

 time within the anterior half of the egg, showing tbe same irregulär 

 arrangement as was at first observed. A little later a cbange begins 

 to take place, it being noticeable that, while predominately irregulär 

 in position, some definite arrangement of the nuclei within the egg 

 is suggested (Fig. 3). As the nuclei increase in number most of tbem 

 move away from their original position wandering towards the sur- 

 face of the egg (Fig. 4); a few, however, remain near tbeir original 

 positions and are thus nearer the median part of the egg than the 

 others. Tbe nuclei can now be divided, although such a division is 

 not as yet well defined, into two groups; one group, the larger, 

 comprising those nuclei, the cleavage nuclei, which have moved 

 furtherest from their original position; the otber, the smaller group, 

 containing those nuclei, the yolk nuclei, which remain nearest the 

 original position. 



At a somewhat later stage it becomes apparent tbat the nuclei 

 are moving more rapidly towards ' the posterior pole than in any 

 otber direction. This is clearly seen by comparing Figs. 2 and 4. 

 If in each of these two figures we would draw a line connecting all 

 of tbe nuclei which are outermost, the outlines thus formed would 

 be quite different, more circular in the first figure, the younger egg, 

 while in the second figure, the outline would more closely follow 

 that of tbe egg itself. Passing on to a still somewhat older egg 

 (Fig. 6) we find tbat tbe arrangement already suggested becomes 

 very pronounced, one group of nuclei, the outermost, arranging 



