﻿Contr. toward the Embryol. and Anat. of Pol. pallipes (Hymenopt.). 131 



It would also sbow the cleavage nuclei a little nearer the anterior 

 tlian the posterior end. Later stages in developraent than have yet 

 been described (Fig. 6) show a much greater number of nuclei in 

 each group, a nearer approach of the zone of cleavage nuclei to the 

 egg's periphery, and a greater regularity in its arrangement. A 

 different arrangement of the zone of cleavage nuclei has been noticed 

 in other Hymenoptera. Carriere and Bürger (11) for Chalicodoma 

 and both Kowalevsky (31) and Dickel (14) for Apis have seen that 

 the zone assumes a pyriform outline the widest part nearest the an- 

 terior pole of the egg. By Polistes, as soon as approximately half 

 of the cleavage nuclei have wandered into the posterior half of the 

 egg, they assume an outline very siniilar to that of the egg. The 

 cleavage nuclei nearest the posterior end travel a much greater 

 distance than do the others. When eggs at a similar stage are cut 

 transversely the zone of cleavage nuclei is seen to lie near the sur- 

 face being evidently at all parts equidistant from it (Fig. 5). There 

 is as yet no intimation as to which surface of the egg will later 

 become ventral or which dorsal. The yolk nuclei are scattered 

 irregulär ly within the zone, but, as in the longitudinal section, there 

 is no regularity in their distribution. Nothing bearing any resem- 

 blance to the rosette arrangement noticed in transverse sections of 

 Dipterous eggs by Kowalevsky (32) and Graber (18) was seen. 

 The entire segmentation in Polistes is very similar to that observed 

 by Henkmg (25) for Lasius and by Dickel (14) for Apis. 



A Keimhautblastem is present in the egg of Polistes and has 

 been previously observed in other Hymenoptem, a number of workers 

 have found it present by Apis, Henking (25) by Lasius, and Car- 

 riere and Bürger (11) for Chalicodoma. The earliest stages of 

 Polistes that we studied showed it to be already present, a thin 

 finely granulated and vacuolated layer, covering the entire surface 

 of the egg just within the egg membranes. Externally it has a 

 distinct boundary but is internally very irregulär, sending numerous 

 processes into the mass of yolk. As the egg develops it increases 

 in thickness, becoming widest just previoiis to the entrance of the 

 cleavage nuclei to form the blastoderm. It is noticeably thicker on 

 the ventral than on the dorsal surface. We at first thought the 

 thickness of the Keimhautblastem could be used in distinguishing the 

 different surfaces of the egg and in judging of its comparative age. 

 This it is impossible to do, the thickness varying nearly as much 

 in eggs of the same age as those in different stages of development, 



9* 



