100 GEORGO ORIHAY SHINJI 



Similarly, the mesoderm keeps pace with the dorsal extension 

 of the ectoderm in the closure of the dorsal wall, as in the case of 

 other insects. 



As the brain gradually grows in size, the amnion, which is 

 situated above, is pushed out until it comes into contact with 

 the serosa, and a rupture occurs at the point of union. Through 

 the rent thus formed, the embryo emerges from the amniotic 

 cavity and begins to rotate around its transverse axis until the 

 poles of the embryo coincide with those of the egg. During this 

 rotation the serosa and the united portion of the amnion shortens. 

 As a consequence, the cells that formed the serosa and amnion 

 aggregate at the dorsal end of the brain as a dense mass of 

 ellipsoidal cells— the dorsal organ. This dorsal organ lasts but 

 a short time, for it soon comes into contact with the invaginating 

 tip of the stomodaeum, where its elongate cells first become 

 disarranged and finally disappear, probably being taken up by 

 the cells of the stomodaeum. 



The exact origin of the mesoderm cells is very difficult to 

 determine in the case of Icerya and Pseudococcus, because of 

 the crowded condition of the cells about the invagination pore. 

 In figure 83 the germ cells and a few entoderm cells are seen, 

 but no mesoderm cells. But in figure 86 there are four kinds of 

 cells, namely, the germ cells, ectoderm, mesoderm, and entoderm 

 cells. Therefore, mesoderm cells must have appeared during 

 the period between these two stages. The way in which the 

 mesoderm forms can, however, be well ascertained in the case of 

 Lecaniodiaspis, where there are comparatively few cells in the 

 early period of invagination. In figure 91 both the amniotic and 

 the ectodermal cells, as well as the mesoderm cells, are all con- 

 nected with the blastopore. This fact, I believe, indicates that 

 not only the mesoderm, but also the entoderm cells are both 

 developed simultaneously with the invagination at the same 

 point, namely, at the tip of the blastopore of Will. In this 

 regard, then,, my observation differs from that of Witlaczil for 

 aphids, where the mesoderm layers are supposed to arise from 

 the ectoderm layer by delamination. Moreover, my interpre- 

 tation of the mesoderm formation is in accord with that of Will 



