DEVELOPMENT 



Amnion and Serosa. Meanwhile, the blastoderm has been folding 

 over the germ band from either side, as shown in Fig. 192, and at length 

 the two folds meet and unite to form two membranes (Fig. 194), namely, 

 an inner one, or amnion, and an outer one, or serosa. 



ac 



FIG. 193. Transverse section of germ 

 layers and amnion folds of Clytra. a, am- 

 nion; e, ectoderm; , inner layer (meso- 

 entoderm); s, serosa. Original, based on 

 Le'caillon's figures. 



FIG. 194. Transverse section of germ 

 layers and embryonal membranes of Clytra. 

 a, amnion; ac, amnion cavity; e, ectoderm; 

 *, inner layer (meso-entoderm) ; s, serosa. 

 After L^CAILLON. 



Segmentation and Appendages. On the germ band, which repre- 

 sents the ventral part of the future insect, the body segments are marked 

 off by transverse grooves (Figs. 195, 197); this segmentation beginning 



FIG. 195. Germ band of a beetle, Lina, in three successive stages. A, unsegmented; 

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

 segments. After GRABER. 



usually at the anterior end of the germ band and progressing backward. 

 Furthermore, an anterior infolding occurs (Fig. 196), forming the stomo- 

 dcBum, from which the mouth, pharynx, oesophagus and other parts of 

 the fore gut are to arise; a similar but posterior invagination, or procto- 

 d&um (Fig. 196), is the beginning, m fundament, of the hind gut. 



