26o THE EMBRYOLOGY OF THE HONEY BEE 



shortens, finally occupying a position in the seventh to the ninth 

 segments inclusive. Meanwhile it loses its attachment to the 

 dorsal splanchnic layer, at the same time receiving an investment 

 of cells from the splanchnic mesoderm lying immediately ventrad 

 of it. This investiture, composed of flat cells then, contracts an 

 adhesion with the ventral border of the heart. 



The mid-intestine is formed from the anterior and posterior 

 mesenteron rudiments in the following manner. The discoid 

 anterior mesenteron rudiment becomes transferred from the ven- 

 tral to the dorsal side of the cephalic pole of the egg by a lengthen- 

 ing of the embryo. At the same time the rudiment increases in 

 superficial area, covering the cephalic end of the yolk like a cap. 

 Its caudal margin now extends rapidly caudad over the dorsal 

 surface of the yolk. Meanwhile the posterior mesenteron rudi- 

 ment has been similarly transferred to the dorsal side of the 

 caudal end of the egg. It now sends out a thin tongue-like pro- 

 cess cephalad over the dorsal surface of the yolk. The caudad 

 extension of the anterior mesenteron rudiment, and the cephalad 

 extension of the posterior mesenteron rudiment next meet on the 

 dorsal surface of the yolk about one-third of the length of the 

 egg from its cephalic pole. The epithelial strip thus formed 

 extends rapidly ventrad over the sides of the yolk until the latter 

 is completely enclosed, the two margins of the epithelium meeting 

 and uniting along the ventral mid-line of the yolk a short time 

 before hatching. Both the fore and hind intestines are formed, 

 as is usual, by ectodermal invaginations. The imagination for 

 the fore intestine, the stomadaeum, is however, not completely 

 ectodermal, since its floor is formed by cells belonging to the 

 anterior mesenteron rudiment, which is not covered by ectoderm. 

 The hind intestine is exclusively ectodermal. The lumen of the 

 stomodaeum (oesophagus) becomes connected with that of the 

 mid-intestine shortly before hatching. A proventricular valve 

 is also formed at this time by folding of the stomodaeal or oesoph- 

 ageal wall. The lumen of the proctodaeum (hind-intestine) is at 

 no time in connection with that of the mid- intestine, both the 

 cephalic end of the hind intestine and the caudal end of the mid- 

 intestine being blind. The four Malpighian tubules are formed 

 as ectodermal invaginations which make their appearance prior to 



