EMBRYONIC DEVELOPMENT OF THE MANTID 229 



The stomodaeum is discernable shortly before the flexing of the 

 telson, while the proctodaeum is visible immediately after. The 

 median groove is now a deep furrow and corresponds with the 

 median longitudinal axis of the embryo. In the meantime the 

 brain has assumed a more definitive outline and the optic plates 

 are differentiating, the nuclei becoming numerous and closely 

 compacted to form a dark band around the lateral margins of 

 the cephalic lobes. The tritocerebrum is recognized as a broad 

 metamere anterior to the mandibular metamere (fig. 3). 



Revolution of the embryo. Up to this point the embryo has 

 been lying on the ventral side of the egg with its longitudinal 

 axis in a straight line. Now a most curious movement may be 

 observed. Its long axis suddenly becomes curved. The head 

 and telson are still directed toward their respective ends of the 

 egg, but the middle of the embryo is bent toward the lateral 

 margin (text fig. 1). This movement is followed by the anterior 

 end of the embryo moving to the side, resulting in slightly 

 straightening the median line. The head is now pointing diagon- 

 ally forward, the thoracic region still exhibiting a slight bending, 

 while the telson alone lies in its original place. The entire 

 embryo then passes laterally around the yolk, maintaining its 

 superficial position, and finally comes to rest on the dorsal side 

 of the egg, the ventral side of the embryo up, while the dorsal 

 side retains its original proximity to the yolk. During this 

 movement, the telson may move rapidly enough to catch up 

 with the anterior end, causing the axis of the embryo again to 

 coincide wdth that of the egg during the remainder of the migra- 

 tion. This is not always so, and the anterior end of the embryo 

 frequently arrives on the dorsal line slightly in advance of the 

 more posterior parts. At different times, during this movement, 

 depending also largely upon the individual case, the median 

 line of the embryo has again become straightened longitudinally. 

 This sometimes occurs shortly after the movement is initiated. 

 In the present study it was found that about three-fourths of the 

 embryos passed around the right side of the egg, but this must 

 not be considered, for the present at least, as indicating any pref- 

 erence in orientation, but rather as an accidental observation 



