DEVELOPMENT 



149 



folding over the germ band from either side, as shown in Fig. 

 190, and at length the two folds meet and unite to form two 

 membranes (Fig. 191), namely, an inner one, or amnion, and 

 an outer one, or scrosa. 



FIG. 192. 



FIG. 193. 



A 



Germ band of a beetle, Melasoma, in three successive stages. A, unsegmented ; 

 B, with oral segments demarkated; C, with three oral, three thoracic and two ab- 

 dominal segments. After GRABER. 



Segmentation and Appendages. On the germ band, 

 which represents the ventral part of the future insect, the body 

 segments are marked off by 

 transverse grooves (Figs. 

 192, 194) ; this segmentation 

 beginning usually at the an- 

 terior end of the germ band 

 and progressing backward. 

 Furthermore, an anterior in- 

 folding occurs (Fig. 193), 

 forming the stoinodaum, 

 from which the mouth, 

 pharynx, oesophagus and other parts of the fore gut are to 

 arise; a similar, but posterior invagination, or proctodccum 



s ' g 



Diagrammatic sagittal section of 

 hymenopterous egg to show stomodaeal 

 (s) and proctodseal (/>) invaginations 

 of the germ band (g). After GRABER. 



