EMBRYONIC DEVELOPMENT OF THE MANTID 233 



serosa, evidently taking up much of the slack in the posterior 

 serosa and, what is perhaps even more important, they are 

 exerting a pull on the amnion in the cephalic area which encloses 

 a large amount of yolk which is to be ingested before closure 

 of the mid-dorsal line. The embryo itself, in its forward growth, 

 is assisting in forcing this mass of yolk back, as it now occupies 

 over two-thirds of the dorsal surface of the egg. The lateral 

 extension of the optic plates, the further differentiation of the 

 buccal segments and nerve centres, with the consequent thicken- 

 ing of this whole cephalic portion of the body, tend to push the 

 yolk back into a less crowded region of the egg. 



The two organs now visible in the serosa are composed of its 

 cells each arranged like a cup around a hollow core. They are 

 tall and columnar in section (text fig. 2, B, C, D, F). Their sole 

 purpose is evidently to further the contraction of the serosa in 

 order to expedite its ingestion within the body cavity with the 

 last of the anterior yolk. The first one has the lumen opening 

 out toward the vitelline membrane. I am convinced that this 

 is the indusium because it has the same cellular structure, oc- 

 cupies the same position as maintained by the indusium in the 

 preceding stage, and finally, because I am unable to find the 

 indusium in any other situation. The second contraction organ 

 is immediately posterior to the first and is composed of cells 

 identical in appearance to those of the remainder of the serosa 

 proper. Its lumen opens toward the dorsal wall of the embryo. 

 As the completion of the dorsal body-wall of the embryo con- 

 tinues, the anterior yolk is pushed posteriorly and ingested in 

 the dorsal thoracic region. The dorsal organ is composed of the 

 serosa, its contraction organs and the amnion. The anterior 

 portion of the amnion is probably the last part to be absorbed, 

 as it immediately precedes the growth of the ectoderm and the 

 mesoderm over the dorsal surface of the head and thorax of 

 the embryo and the rapidity of its movement is therefore depend- 

 ent upon the rate of growth of these embryonic tissues. 



A late embryonic envelope. Just before hatching the embryo 

 secretes the chitinous epidermis (fig. 9). Each of the appendages 

 thus becomes individually incased so that they are all separated 



