254 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



Segmentation of the germ band begins about the time the proctodaeum 

 forms. Twenty-one segments are evident: one oral, one intercalary, one 

 antennal, three gnathal, three leg, eight abdominal, and four proctodaeal 

 segments, the last four later fusing into an anal segment. The intercalary 

 segment is less distinctly developed than the others. The mandibles 

 are smaller than the maxillae which in turn are smaller than the paired 

 second maxillae (labium). According to Scholzel (1937), the hypo- 

 pharynx is a derivative of the sternum of the mandibular and first maxil- 



myct 



enim- 



emb 



ser 



Fig. 177. — Pediculus. Sagittal sec- 

 tion, {am) Amnion, {emb) Embryo. 

 ientm) Ental membrane, {myct) Myce- 

 tom. {ser) Serosa. 



Fig. 178. — Pediculus. Sagittal sec- 

 tion of embryo during revolution, {am) 

 Amnion. {entm) Ental membrane. 

 {gl) Prothoracic gland shortly before 

 degeneration, {myct) Mycetom. {ser) 

 Serosa. 



lary segment. This is not in agreement with the interpretation of 

 Fernando (1934). 



The germ band, which in the stage shown in Fig. 176 is attached to the 

 serosa, becomes free (Fig. 177) by the time the segmentation is recogniz- 

 able and the anlagen of the appendages appear. The amnion separates 

 the germ band from the yolk on the ventral side. Dorsally it is separated 

 from the yolk by a membrane that is fused with the posterior part of the 

 head of the embryo and at the caudal end with the proximal part of the 

 hind-gut (Fig. 177, entm). In cross section it appears that in the middle 

 section of the body the amnion and the dorsal membrane ("ental mem- 

 brane") just mentioned arise from the same lateral region of the germ 

 band. Revolution of the embryo is initiated by a secondary fusion 

 of the amnion with the serosa at the place where the original invagination 



