88 THE EMBRYOLOGY OF THE HONEY BEE 



is finally torn by the active movement of the young larva." The 

 writer has not observed this process in the living larva, but a 

 study of sections confirms Biitschli's statements. Up to Stage 

 XIV the amnion is intact, but at Stage XV, when the young 

 larva has become flexed ventrad, and has ruptured the chor- 

 ion, the amniotic membrane is evident only in fragments, 

 usually clinging to the chorion. These fragments or shreds are 

 very much thicker than was the amnion before its rupture, and 

 always contain a number of ovoid nuclei, closely grouped to- 

 gether, indicating that the fragments had contracted and sug- 

 gesting that the amnion had been under tension previous to its 

 rupture. In Chalicodoma, according to Carriere (1890, 1897) 

 some time before the hatching of the larva the embryonic envelope 

 becomes torn into fragments, which become thickened to form 

 narrow twisted bands of polygonal cells. These disappear before 

 hatching, being apparently absorbed. In the pterygote insects 

 of other orders, — Orthoptera, Coleoptera — the later history of 

 the embryonic envelopes is very varied, and usually associated 

 with a shifting in the position of the embryo relative to the yolk 

 (blastokinesis, Wheeler 1893). The fate of these envelopes, 

 briefly stated, is as follows : The serosa is either cast off or ab- 

 sorbed by the egg ; the amnion is usually also absorbed, but in some 

 cases has been described as contributing to the formation of the 

 dorsal body wall, as in Meloe (Nusbaum 1890). 



2. The Cephalo-dorsal Body 



Associated with the formation of the amnion and contempor- 

 aneous with that of the germ layers, is a peculiar structure to 

 which the writer (1912) gave the name "cephalo-dorsal disk." 

 This structure (Fig. 34 A-C), which attains its maximum size 

 about Stage V, is extremely variable in location, form and size. 

 On account of its variability in size it would be better to term this 

 structure the "cephalo-dorsal body." It is situated on the dorsal 

 side of the egg usually near the cephalic pole and opposite to the 

 anterior mesenteron rudiment (Fig. 34A), but in one egg, which 

 appeared to be normal in every other respect, the cephalo-dorsal 

 body was found situated almost precisely at the cephalic pole it- 

 self. The form of this body, while very variable, usually ap- 



