7 2 WHEELER. [Vol. VIII. 



sition of yolk at the lower pole, this movement has been 

 deflected. 



Melanoplus fcmiir-i'iibrmn was studied as a representative of 

 the Acrididae. The germ-band is formed very near the caudal 

 pole of the &%%, but still on the convex ventral surface. During 

 the formation of the envelopes the posterior end of the body 

 grows around the pole onto the dorsal surface, while its head 

 remains fixed at the pole. It is not until the germ-band has 

 reached a stage corresponding to Stage F. in XipJiiditim that 

 its head leaves the pole and the whole body moves upward on 

 the dorsal surface. It soon comes to a standstill and passes 

 the winter in this inverted position. In the spring it moves 

 back around the lower pole and, like the Gryllid and Locustid 

 embryo in a corresponding stage, proceeds to lengthen and en- 

 velop the yolk till its head reaches the cephalic pole, 



Packard ('83) seems to have been the first to study the devel- 

 opment of Acridians {MelanopliLs sprehis and M. atlanis). But 

 he had no conception of the true relations of the embryo to the 

 yolk, as is shown by his Fig. i, PI. XVII, where the ^gg is 

 depicted with the micropylar end uppermost. Leuckart ('55) 

 long ago showed that the Acridian micropyle is located at the 

 caudal pole. If the Q.gg figured by Packard be inverted, it will 

 represent the embryo on the point of undergoing katatrepsis. 



The same error is committed by Graber in his accounts 

 of StenobotJirus variabilis ('88, '9o). Misled, like Packard, by 

 the position of the micropyle, he has mistaken the caudal for 

 the cephalic pole. To mean anything his figures must be in- 

 verted. As I have not yet studied the later stages of Melan- 

 oplus in section, I will not attempt to describe the details of 

 katatrepsis. Graber claims to have observed that the pleural 

 ectoderm, where it passes into the amnion proliferates a thin 

 cell-lamella to form the dorsal wall, while the amnion remains 

 intact and still covers the ventral face of the embryo. This 

 account is not substantiated by his figures (i and 2, PI. I). 

 The two thin cell-lamellae extending over the dorsal surface 

 have every appearance of being the walls of the heart, and 

 therefore mesodermal, although it is difficult to see how this 

 organ could be so completely formed in so early a stage. As 



