286 



INSECTA. 



caudal amniotic fold (Fig. 143 4). This process has been described 

 by Kowalevsky for Apis, and still more clearly by Graber for 

 Polistes gallica and Formica, and more recently for Hylotoma 

 berberidis (Xos. 27 and 30). In Apis, at least, the cephalic fold 

 seems to take a greater share in the overgrowth of the germ-band 

 than the caudal fold. 



X 



an 



Fig. 143. — Diagrammatic median sections of two stages of development of Hylotoma berberidis 

 (after Graber). «i-«i", first ten abdominal segments ; am, amnion ; an, anus ; at, antenna ; 

 bg, ventral chain of ganglia ; do, food-yolk ; ed, proctodaeum ; m, mouth ; md, mandible ; 

 mxi, first maxilla; mx?, second maxilla; 03, supra-oesophageal ganglion; ol, labrum ; 

 pi, p2 ] l S i the three thoracic limbs ; s, serosa ; sp, salivary glands ; vd, stomodaeum x, x 1 , 

 point at which the amnion passes into the ectoderm. 



The germ-band in the Hymenoptera remains as a mle comparatively short. 

 It is not longer than the egg (Fig. 143 A), and thus remains restricted to the 

 ventral side. On the other hand, the amniotic cavity itself continues to extend 

 over the anterior and posterior ends of the germ-band towards the dorsal 

 surface, thus causing the points where the amnion unites with the ectoderm of 

 the germ-band (a; and x') gradually to approach one another, a rare condition 



