THE EMBRYOLOGY OF THE HONEY BEE 105 



The three pairs of leg rudiments are plainly outlined and consti- 

 tute low rounded protuberances. The ventral nerve cord is now 

 distinctly visible, on ventral view appearing as a dark band, seg- 

 mentally enlarged, and pierced intersegmentally by oval openings. 



The tracheal system is well on its way to completion, as indi- 

 cated by the completion of the ventral tracheal loops (TraCom) 

 which are plainly seen on ventral view as delicate sharply outlined 

 tubes. 



The silk glands and the Malpighian tubules, the latter no longer 

 visible from the ventral side, have continued to increase in length. 



Stage XIII. Estimated at 62-64 hours (Fig. XIII). The 

 changes of most importance at this stage concern the antennae 

 and mouth parts. The former are less prominent than at Stage 

 XII, and are in fact in process of disappearing. Both the man- 

 dibles and first maxillae are bluntly conical in form and directed 

 inwards and forwards. The second maxillae have drawn still 

 closer together, and are becoming united to one another by their 

 mesial borders. At the same time the two external openings of 

 the silk glands are also brought close together. The second maxil- 

 lae unite by their edges only, overarching, as it were, the inter- 

 vening space on which the silk glands open, and which, after the 

 completion of the fusion of the second maxillae, becomes the 

 common unpaired duct of the silk glands which ultimately opens 

 at the tip of the labium. 



Stage XIV. 66-68 hours (Fig. XIV). At this stage the de- 

 velopment within the egg is virtually completed. The principal 

 changes to be noted are : the almost total disappearance of the 

 antennal rudiments, of which only the faintest vestiges remain 

 visible on the exterior, and the completion of the union of the 

 second maxillae to form the labium. At 76-78 hours, eight hours 

 later — the embryo will rupture the chorion and elongate, being at 

 the same time flexed in a direction opposite to that of the embryo, 

 and become a young larva (Fig. XV) whose structure has already 

 been described. 



3. Segmentation 

 It is generally believed by students of invertebrate morphology 

 that insects as well as other arthopods are made up of a linear 

 series of serially homologous segments, which in the primitive 



