250 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



invagination abutting on the anterior entoderm rudiment. Cells of the 

 middle entodermal mass arrange themselves in the form of a layer 

 between the nutritive yolk mass and the mesodermal cells on the ventral 

 side. In the nutritive mass are entodermal cells as well as trophocytes 

 (vitellophags). Stomodaeum and proctodaeum are surrounded by 

 mesodermal cells from which the muscles arise. The anterior entoderm 

 rudiment becomes arranged in a layer that, in conjunction with the blind 

 inner en(^ of the stomodaeum, forms a small vesicle, or sac (Fig. 171), 

 projecting into the nutritive mass. A similar but much smaller sac 

 appears at the blind end of the proctodaeum. Amnion and serosa by 

 this time have disappeared entirely, though Fernando (1934) does not 



stom 







.«S:'?' 



^« \35" 



■si^iri .m^ 







Fig. 171. — Archipsocus. Sagittal section of stomodaeum (stom). {br) Brain, (ent) 

 Entoderm, {mes) Mesoderm, (ser) Serosa, (trc) Trophocyte. (ves) Vesicle. 



state in what manner this is accomplished. The dorsal organ lies above 

 the stomodaeum. Between the dorsal organ and the brain is the remnant 

 of the anterior entodermal mass loosely adherent to the dorsal surface 

 of the stomodaeum. Along the ventral surface of the nutritive mass 

 is the layer of entodermal cells from the middle rudiment. Meanwhile 

 dorsally the entodermal cells in the nutritive mass arrange themselves 

 in a dorsal layer. The nutritive mass is thus gradually enclosed by ento- 

 dermal cells (Fig. 172) with the help of the entodermal cells situated 

 at the tip of the proctodaeum. At this time the mid-gut is attached 

 to the stomodaeum, and internally the mid-gut encloses the anterior 

 entodermal vesicle (Fig. 172, ent. ves) which was derived from the major 

 part of the anterior entodermal rudiment. The vesicle elongates toward 

 the posterior end where it comes in contact with the smaller posterior 

 vesicle, thereby forming a tube. Meanwhile the nutritive mass is 



