7 6 WHEELER. [Vol. V 1 1 1 . 



to the dorsal surface, but soon separates from the serosa so 

 that a small amount of yolk is enclosed between the two en- 

 velopes. Later the yolk is expelled from this region and the 

 envelopes become applied to each other. A true movement 

 then sets in and carries the anterior portion of the germ-band 

 forward up the ventral surface till the procephaleum overlaps 

 the cephalic pole {Cf. Heider's figures, 4 ^, 6 a, y a and 9, 

 PI. II. ('89). A certain similarity of these movements to those 

 exhibited in Blatta leads me to believe that they represent 

 a weakened blastokinesis. 



Whether or not similar movements occur in the other so- 

 called " ectoblastic " forms (DijDtera, Hymenoptera, Siphonap- 

 tera, Neuroptera, Trichoptera) cannot be decided at present. 

 If such movements occur at all they are probably exceedingly 

 weak. 



As stated above, the Lepidoptera have developed embryonic 

 movements peculiar to themselves. In all the members of the 

 order hitherto studied, the germ-band arises on the ventral sur- 

 face of the Q%^, and its envelopes are formed while it is still 

 in this position. As development proceeds the convex ventral 

 surface of the germ-band, with its adherent amnion, moves back 

 from the ventral serosa and soon comes to lie in the middle of 

 the yolk. Hereupon the ventral surface of the embryo be- 

 comes concave, and its dorsal surface is applied to the dorsal 

 serosa. I have already remarked that this movement of the 

 embryo may have been independently developed for the same 

 purely physiological purposes as blastokinesis in the Homo- 

 morpha. The fact that the movement is represented in the 

 Trichoptera only by the change in flexure of the longitudinal 

 embryonic axis, would seem to indicate that it has been 

 acquired since the Lepidoptera diverged from the Trichopteroid 

 ancestor. 



Graber ('9o) has recently made the interesting discovery that 

 the Phytophagous Hymenoptera closely resemble the Lepidop- 

 tera in the movements of the embryo and in the amputation of 

 the envelopes. This, taken together with the striking resem- 

 blance between the cruciform larvae of the two groups, appears 

 to point to a closer relationship than has usually been claimed. 



