THE EMBRYOLOGY OF THE HONEY BEE 83 



strip, which becomes submerged in the yolk (Figs. 20A and B, 21, 

 24B, 34B and C, Am). Subsequently then is a fusion of the 

 amniotic bands along the dorsal mid-line of the egg, beginning 

 first at the cephalic end, and occurring somewhat later over the 

 remaining extent of the egg, being completed at Stage VI. 



While the amnion is thus covering the dorsal side of the yolk 

 it commences also to cover the ventral side. This process can 

 best be observed in fresh material, in which the outlines of the 

 amnion are beautifully clear. In fixed material, whether examined 

 in alcohol or stained and cleared, the outlines of the amnion are 

 frequently invisible, except in actual or optical sections. At Stage 

 V or a little earlier, on the ventral side of the egg, the amnion 

 together with the anterior end of the germ band separate from the 

 yolk (Fig. 26A). This is not primarily due to the depression of 

 the yolk caused by the development of the anterior mesenteron 

 rudiment as the figure might suggest, since the separation is al- 

 ready evident when this rudiment is in its earliest stages ; it is 

 probably first brought about by an increase in the superficial extent 

 of the amnion in this region, as indicated by its convex or arched 

 form. Soon after, the amnion separates from the yolk over the 

 entire cephalic pole of the egg, rising up in the shape of a hemi- 

 spherical cap (Fig. V). Next — at Stage VI — it severs its con- 

 nection with the germ band around the anterior end of the latter 

 and slides over it in the form of a hood or cowl, thus forming the 

 cephalic fold (Fig. 32, iam, and 26B Am). This separation of 

 the amnion from the germ band progresses caudad along its 

 lateral margins, accompanied by the caudad extension of the ceph- 

 alic fold over the ventral face of the germ band in such a way 

 that the free edge of the cephalic fold forms a semicircular curve 

 with its concave side directed caudad (Fig. 32, A-C, iam). When 

 the cephalic fold has covered about one-half of the ventral face 

 of the embryo, a second amniotic fold, the caudal fold (Fig. 32 

 B, 2am), appears at the extreme caudal end of the germ band. 

 This fold is formed like the head fold, by separation of the am- 

 nion from the caudal end of the germ band, and first appears as a 

 crescentic membrane. Since the caudal end of the germ band is 

 now curved completely around the caudal pole of the egg, so that 

 the former lies on the dorsal side of the egg, the caudal fold also 



