﻿Contr. toward the Embryol. and Anat. of Pol. pallipes Hynienopt.;. 139 



a great difference is here noticeable in the fact that Graber (18) 

 found, in the eggs of this Dipteron, the Keimhautblastem to be absent. 

 If we compare the figures we have just described with any of the 

 blastoderm cells, it will be seen that the amount of protoplasm 

 surrounding the nucleus is much smaller than the amount within the 

 cell. An inner Keimhautblastem is not present immediately after the 

 formation of the blastoderm, and in no sections did we notice a 

 continuous layer just within the blastoderm. We do find, after 

 completed formation of the blastoderm, irregulär patches of a rather 

 finely granulated mass at the base of some of the blastoderm cells. 

 We will shortly show that the cleavage nuclei, after reaching the 

 inner surface of the Keimhautblastem, push on through it until they 

 reach a position near its outer surface. The migration of these 

 nuclei to the egg's surface is undoubtedly due, at least the active 

 part of it, to the cytoplasm which surrounds them. The pseudo- 

 podial-like processes possessed by these masses of cytoplasm, are 

 used to partially envelope the yolk globules and expose a greater 

 amount of their surface to them, and they are also used in locomotion. 

 When the nuclei reach the Keimhautblastem they move into it, and 

 this locomotion, it seems to us, is easier explained if the two, nucleus 

 and cytoplasm, continue intact. The immediate fusion of the cyto- 

 plasm with the Keimhautblastem would compel the nuclei to be 

 themselves the active agency in their further progress. 



The nuclei pass on into the Keimhautblastem until about two- 

 thirds of the distance from the inner to the outer surface has been 

 traversed; here their migration ceases. We have often noticed that 

 many nuclei, after they have entered the Keimhautblastem, lengthen, 

 their longitudinal axis then being at right angles to the eggs surface; 

 this is not constant, and is seen only in a few nuclei. A somewhat 

 similar elongated nucleus has been observed by Blochmann (2), 

 Henking (25), Kowalevsky (31) and Noack (42) as occurring either 

 in an early or late pre-blastodermic stage. All these observers, 

 however, figured the nucleus as cuneiform with the truncated end 

 towards the surface of the egg. When in Polistcs the nuclei have 

 pushed partly through the Keimhautblastem there follows a. period 

 during which it recedes from the egg membranes, not at all points, 

 but between the nuclei, giving the surface an undulating appearance. 

 The egg in surface view appears very similar to a blastula of Amphi- 

 oxiiSj each protruding part enclosing a nucleus, but no cells have as 

 yet formed. A similar appearance has been described and figured 



