^O WHEELER. [Vol. VIII. 



mio-ratc to some other surface. This, of course, necessitates a 

 secondary union of the envelopes previous to katatrepsis. 



The hypothesis set forth in the preceding paragraphs is also 

 supported indirectly by the fact that in the eggs of the Meta- 

 bola which are less abundantly provided with yolk than the 

 eggs of the Ametabola, blastokinesis is either faint or wanting. 

 Aeration would be much less necessary in such small eggs. 

 The lengthening and shortening movements seen in the 

 embryos of the Metabola as well as in those of the Ametabola 

 may suffice to keep the yolk circulating. The Lepidopteran 

 germ-band, it is true, exhibits movements, but the eggs of 

 these insects are laid in exposed situations and provided with 

 unusually thick envelopes, so that the movements of the em- 

 bryo, though differing widely from the typical blastokinesis of 

 lower forms, have perhaps been independently acquired for a 

 similar purpose. 



I had intended to give a comparative description of blasto- 

 kinesis in the different orders of insects but as the known 

 facts have been recently summarized in a masterly manner 

 by Korschelt and H eider ('92) I shall confine my remarks 

 mainly to the Orthoptera. Although Graber, Ayers and 

 others have studied representatives of this very important 

 group, they have given but fragmentary and often inaccurate 

 accounts of the relations of the embryo to the yolk-mass at 

 different periods of development, 



I may begin my account with the Saltatoria which comprise 

 the three families Gryllidse, Locustidse and Acrididae. As 

 representatives of the first, Gryllus htcttiosiis and CEcantJms 

 niveus were studied. In both of these insects as was pointed 

 out at p. 42 the germ-band arises on the ventral surface of 

 the yolk near the caudal pole. During the formation of the 

 envelopes anatrepsis sets in and carries the germ-band to the 

 dorsal surface where it rests through the winter in an inverted 

 position with its head directed to the caudal and its tail to the 

 cephalic pole. In the spring the envelopes over the head end 

 first fuse and then rupture ; the embryo is thereupon everted 

 and during katatrepsis passes around the caudal pole to regain 

 its upright position on the ventral yolk. The envelopes during 



