﻿Contributions toward the Embryology and Anatomy of 

 Polistes pallipes (Hymenopteron). 



I. The Formation of the Blastoderm and the first Arrangement 



of its Cells. 



By 



William S. Marshall and Paul H. Dernehl. 



With Plates X and XI. 



Historical. 



The earlier students of insect embryology were at a great 

 disadvantage in their work in having to study the egg entirely from 

 an external view ; there was hidden from them, either entirely or in 

 part, much that has since been observed. By crushing the egg cer- 

 tain observations were made as to the presence of nuclei or cells 

 within it, a use of transparent eggs led to similar conclusions; this 

 could only lead at first to a supposition that these had anything to 

 do with the cells which later were seen to appear upon the egg's 

 surface. The use of the microtome and modern methods of staining 

 necessarily gave to all later students a means of ascertaining what 

 took place within the egg, also of following the changes and con- 

 nectiDg them with each other. It appears, however, in insect em- 

 bryology, as with so many other branches of zoology, that the 

 earliest workers gained a surprising knowledge of their subject. 

 Before it was conclusively shown that the first segmentation nucleus 

 gave rise by division to the nuclei which later took part in the 

 formation of the blastoderm cells, this was held by some to be their 

 origin, and the later works have given us details but few general 

 conclusions concerning the development of the insect's egg. 



Historically considered, the pre-blastodermic development of the 

 Hymenoptera would be short, and it seems to us best to give a 

 general account of what was known concerning the early development 



