﻿Contr. toward the Embryol. and Anat. of Pol. pallipes (Hymenopt.). 143 



number of these dividing blastoderm cells, and would call attention 

 to two points, namely, the entire absence of direct division and to 

 the fact that the divisions do not occur in any particular direction 

 relative to the surface of the egg. Petrunkewitsch (45) figures a 

 portion of the blastoderm of the honey-bee, showing the nuclei 

 dividing in different planes. Many observers have, however, recorded 

 observations directly opposed to these, and held that the blastoderm 

 cells do all divide in some one definite direction. Grimm (20) says 

 that in the eggs of Chironomus the blastoderm cells divide »in der 

 Eichtung der Eiradien«. Tangential division of these cells has been 

 recorded by Blochmann (2), Wheeler (60) and Heymons (26). Here 

 and there in the blastoderm, bi-nucleate cells were observed, although 

 never occurring abundantly. Bütschli (9) and Wheeler (60) have 

 recorded a similar occurrence. To gain some idea of the direction 

 in which blastoderm cells divide we selected an egg in an early 

 blastoderm stage, one cut transversly, and, examining one-third of 

 the sections, marked the direction of division in each dividing cell. 

 In Fig. 43 we give the result, the longer lines representing each a 

 longitudinal axis of a mitotic figure, the small transverse lines the 

 Position of the chromosomes, the long line above these the snrface 

 of the egg. It will be noticed that the equatorial plate stage occurs 

 much oftener than any other. 



We have now reached a stage in the development of the egg 

 of Polistes in which the blastoderm cells have been forined as a 

 Single continuous layer over the surface of the egg. What changes 

 next take place, while they may have, by a further division of the 

 cells and an increase in their number, something to do in altering 

 the blastoderm. yet really have more to do with the first arrangement 

 of the cells in the formation of the germinal band. 



The first arrangement of the blastoderm cells. 



The various shapes and sizes assumed by the blastoderm cells 

 on the different parts of the eggs surface have been noted by a 

 great many observers, and to give all the variations in shape and 

 size which each one has recorded, would require a citation from 

 nearly all of the works noted in the bibliography as well as several 

 which have been omitted. We can say in general that the blasto- 

 derm cells, after being formed, soon change their shape and their 

 size, the surface of the egg becomes covered by a layer of cells 

 showing inequalities in their form and in their mass. A final result 



