﻿Contr. toward the Embryol. and Anat. of Pol. pallipes (Hymenopt.). 129 



themselves in a zone or belt with an outline very similar to that of the 

 egg*, a second group, the nuclei of which reniain near the center of 

 the egg and show a very irregulär arrangement. Those of the first 

 group, the cleavage nuclei, and those of the second group, the yolk 

 nuclei, both add to their number by mitotic division. 



As just mentioned all the nuclei present possess the power of 

 dividing mitotically and are as yet different from each other only in 

 their position within the egg. There now appears a difference in 

 the secondary origin of the various nuclei. The cleavage nuclei, 

 when clearly defined as such, increase only by mitosis of nuclei 

 belonging to this group; the yolk nuclei increase by mitotic divisions 

 of their own number and also in the following manner. As the 

 cleavage nuclei wander towards the periphery of the egg a few drop 

 behind and add themselves to the second, inner group, the yolk 

 nuclei. Sections of eggs showing the zone of cleavage nuclei well 

 out towards the periphery would show nuclei just within the zone 

 and at some distance from most of the yolk nuclei. We could see 

 no indication that these nuclei ever rejoined the zone, and, as yolk 

 nuclei are in later stages present in this same part of the egg, it 

 appeared most probable that these nuclei, whose origin was from 

 the nuclei of the zone, remained in the yolk and became yolk nuclei. 



The division of nuclei within the egg and the fact that they 

 all came originally from the first segmentation nucleus has been 

 known for some time, Metschnikow (41); the question concerning 

 the kind of division being, however, a subject of dispute. Witlaczil 

 (62) found for the eggs of Aphis that the nuclei within the egg 

 divided amitotically his figure showing a nucleus of a » biskuitförmige 

 Gestalt«. iiccording to Will (61), the division of the cleavage nuclei 

 occurs mitotically. In 1889 Heider (23) for Hydrophilus and Wheeler 

 (60) for Blattei and Boryphora described the division as mitotic. 

 Cholodkowsky (13) described amitosis as occurring in the yolk nu- 

 clei of Phyllodromia, Schwartze (51) holding that in Lepidoptera 

 division is not always the same, occurring mitotically in the cleavage 

 nuclei but not discovering any mitotic figures in those nuclei within 

 the center of the egg. Heymons (26) found mitosis in the cleavage 

 nuclei in some Orthoptera, but in Forficula a direct division of the 

 yolk nuclei. Tschüprofp (35) distinguishes two kinds of nuclei in 

 the eggs of Odonata, the one kind dividing by mitosis, the other 

 amitotically. Carriere and Bürger (11) found that the yolk nuclei 

 of Sialis divided amitotically. These latter for Chalicodoma, and 



Zeitschrift f. wissensch. Zoologie. LXXX. Bd. 9 



