﻿Contr. toward the Enibryol. and Anat. of Pol. pallipes (Hymenopt.) 123 



of insects prior to the advent of modern metliods of research. Our 

 account is not perfect, a number of references not being at our 

 disposal, and, in some few instances, cited results have been taken 

 from other papers. 



Herold and Eölliker (29) were two of the first, wliose obser- 

 vations on insects eggs could be said to have any embryological 

 bearing. Köllikers work, which appeared in 1842, was written 

 from observations on Chironomus, Simulia and Donacia. He un- 

 doubtedly observed a blastoderm surrounding the Dipterous egg, 

 which covered the entire yolk mass. The nucleated cells of this 

 peripheral layer increased in number, becoming sm aller and finally 

 showing more than a Single layer. Burmeister (8), studying the 

 eggs of Palingenia, found a layer of unequal thickness on the sur- 

 face of the egg, probably the Keimhautblastem. He also saw, 

 although Zaddach (63) disagrees with this Statement , a blastoderm 

 which covered two-thirds of the egg, developing on the third day. 

 Leydig (38), figured the ovarian tubules with enclosed eggs of Aphis, 

 and figured an early stage containing a number of large nuclei within 

 the egg; in a later stage these are shown nearly surrounding it, 

 occupying a position that would correspond to the blastoderm cells, 

 or rather the nuclei of them. 



Zaddach's (63) paper, published in 1854, on the development of 

 the Phryganids, was much more of an attempt than had yet been 

 made to work out the embryology of any insect. He followed the 

 development through, and than gave considerable Space to the dis- 

 cussion of questions having a general and a comparative interest 

 He first describes the appearance, at the periphery of the egg, of 

 numerous »Punkte und Stellen« from which the yolk withdraws and 

 they then flow together, forming a broad peripheral zone over the 

 egg; this is clearer and more finely granulated than the other Con- 

 tents of the egg. We are unable to make out just what Zaddach 

 meant; he undoubtedly describes here the Keimhautblastem, but 

 forming in a peculiar way, There next appears a number of round 

 »Flecke«, in this peripheral layer, which are the first blastoderm 

 cells ; these are nucleated and Surround the egg in a continuous Single 

 layer. The cells are at first nearly Square, but change by a round- 

 ing-off of the corners. Zaddach describes these blastoderm cells 

 as remaining large over the ventral surface but disappearing dorsally. 



A paper by Huxley (27) in 1857, gives a figure of an Aphis 

 egg showing a peripheral layer of large nuclei, which, on one side 



