No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 43 



arise on the concave face of the ^gg. The germ-band of 

 GLcantJms, like that of Giylhis, first makes its appearance as a 

 thickening of the blastoderm on the convex surface near the 

 lower pole of the ^gg. This convex surface is, therefore, the 

 ventral surface and the micropyle marks the " primitively head- 

 end " of the ^gg as is shown by the fact that the procephaleum 

 is originally directed towards this and not towards the opposite 

 pole, which Ayers incorrectly calls the "primitively head-end." 

 The germ-band, however, soon leaves its position on the convex 

 ventral surface and, moving around the lower pole tail first, 

 comes to lie on the concave dorsal yolk. It is clear that Ayers 

 could not have seen the stages preceding the arrival of the 

 germ-band on the dorsal surface, and it is during these very 

 stages that the blastopore forms and closes. 



Before turning the lower pole the germ-band of Qicanthns 

 resembles that of Stagmoniaiitis. Its anterior is distinctly 

 wider than its posterior end and represents the future pro- 

 cephalic region. A narrow, but distinct groove runs from the 

 oral to the anal end as in the forms we have been considering. 

 At the posterior end the groove bifurcates much as in 

 XipJddiiun. That this median groove gives rise to the mesen- 

 toderm admits of little doubt after what has been said of other 

 Orthoptera. The amnio-serosal fold appears to arise simul- 

 taneously along the entire margin of the germ-band as in 

 Grylhis. 



It follows from the observations here recorded, fragmentary 

 as they are in many respects, together with Graber's observa- 

 tions on StcnobotJirus, that the Orthoptera can no longer be 

 regarded as Jiors de ligiic so far as the formation of their 

 germ-layers is concerned. In all the families of the order, 

 save the Phasmidae, an invaginate gastrula has been found, 

 and there can be little doubt that the investigator who 

 is so fortunate as to study embryos of this family will find in 

 them essentially the same process of germ-layer formation. 



