l6 THE EMBRYOLOGY OF INSECTS AND ARACHNIDS. 



The upper lip is double and the antennae have the same position as in Thyri- 

 dopteryx and Chrysopa. 



ORTHOPTERA. 



Mantis and the grasshopper were the orthopterous insects studied. 



The early stages in the development of Mantis were obtained and the latter 

 stages in the development of the grasshopper. The developmental history of the 

 group derived from the study of both insects is not complete, though some obser- 

 vations of importance were made. 



At the earliest stage obtained, the egg of the grasshopper consisted of large 

 angular yolk masses like those of the spider (Fig. XLV). The yolk is enclosed by 

 a very thick membrane with concave hexagonal depressions on its outer surface 

 (CH, Fig. XLV, XLVI). Within this outer chorion there is another thinner mem-, 

 brane. 



In what is apparently the earliest stage, a portion of the yolk is much vesicu- 

 lated (E' Fig. XLV). Near or in this portion of the yolk a few nuclei occur, (YC, 

 Fig. XLV). At what appears to be a later stage, the yolk consists of pyramids with 

 their apices at the centre of the egg. On the bases of the pyramids at the surface 

 of the egg are nuclei or nucleated cells. Within the yolk at this stage, no nuclei 

 were found, though they might have been present and have escaped observation, as 

 the sections were in many cases considerably broken. 



Later in development the yolk pyramids break up. This breakage is probably 

 effected by the vesicles in the pyramids uniting and consequently causing a sepa- 

 ration of the yolk substance along the line of their union. 



These pyramids recall the yolk pryamids of Astacus, described by Reichenbach. (1) 

 They might also be compared to the yolk columns described by Ludwig ( '~' for the 

 spider's egg. Other investigators, however, have not confirmed Ludwig's obser- 

 vations, but find that all the cells are not at the surface, as he claimed, but that some 

 remain centrally located in the yolk. The yolk of the Mantis egg is very like the 

 yolk of the grasshopper egg. The yolk of the higher orders of insects studied, con- 

 sisted of rounded spherules which were often much vesiculated. 



(i) Die Embryoanlage u. erste Entwicklung d. Flusskrebses. Zeit f. wiss. Zool. Vol. XXIX. 

 (-) Ueber die Bildung des Blastodermes bei den Spinnen. 



