5 WHEELER. [Vol. VIII. 



on the median portions of the Qgg till they become very diffi- 

 cult to resolve. They evidently coincide with the areas covered 

 by the polygonal cells of the follicular epithelium. 



No traces of micropyles could be found. Their absence in 

 Xiphidmni is of interest, since Leuckart (-55) long since 

 described and figured them in several European Locustidae 

 {Mcconenia, Decticits, Locusta, Ephippigerd) . In these genera 

 they consist of funnel-like perforations on the ventral surface 

 of the chorion either near the anterior pole or nearer the 

 middle of the ^gg. 



The preblastodermic stages were not studied. They prob- 

 ably resemble the corresponding stages of Blatta, of which I 

 have given a detailed account in a former paper ('89). 



When fully formed the XipJtidhim blastoderm, like that of 

 Blatta, consists of a thin sheet of cells, that have in part 

 reached the surface from the interior of the Qgg, and are in 

 part derived from these centrifugal cells by tangential division 

 after their arrival at the surface. Numerous cells — the future 

 vitellophags — are to be found at different points in the yolk. 

 Whether they are derived from the incompleted blastoderm 

 by centripetal division, or are inhibited before reaching the 

 surface, my limited observations will not permit me to decide. 



The cells forming the blastoderm are polygonal, much flat- 

 tened and of uniform size and distribution. Those on the 

 center of the convex, or ventral face of the Q,gg soon begin to 

 change their dimensions; from being broad and flat, they 

 become more nearly cubical, their lenticular nuclei again 

 assuming the spherical or oval shape which they had in 

 preblastodermic stages. These changes take place over a 

 limited and somewhat oval area and result in the formation of 

 the ventral plate. The few eggs that I have been able to find 

 in the very first stages after the completion of the blastoderm 

 leave me in some doubt as to the exact process whereby the 

 embryo is established. I am satisfied, however, that the 

 thickening and narrowing of the individual blastodermic cells 

 does not take place simultaneously over the whole ventral 

 plate area, but that there appear, as in the crustacean egg {e.g. 

 Astacus, Homanis), several discrete centres about which the 



