THE EMBRYOLOGY OF THE HONEY BEE 103 



what enlarged and flattened at the tip, like a pestle. The rudi- 

 ments of the legs are now apparent as low rounded elevations in 

 line with the mouth parts. The first pair are fairly well defined, 

 the second and third pairs are faint, the last especially so. The 

 germ band as a whole has increased considerably in width, now 

 covering a trifle over a half of the entire surface of the yolk, 

 and is divided by slight constrictions into thirteen segments, the 

 definitive number. 



The silk glands have lengthened to slender tubes extending cau- 

 dad to the sixth trunk segment. 



The openings of the tracheal invaginations, the future spiracles, 

 are now small round aperatures and by the widening of the germ 

 band have been carried so far laterad as to be virtually invisible 

 from the ventral surface. The invaginations themselves have 

 increased in size and extent and form flat sacs lying close against 

 the inner surface of the ectoderm. 



The proctodaeal imagination (Pro) has made its appearance 

 as a funnel-shaped depression just dorsad of the caudal pole of 

 the egg while the Malpighian tubules (Mai) are seen as two pairs 

 of short blind tubes arising from its base. 



Stage XL Estimated at 56-58 hours (Fig. XI). The general 

 appearance of this embryo is very similar to that of the stage 

 preceding. The swellings representing the tritocerebrum have 

 totally disappeared. The germ band covers a little over one-half 

 of the circumference of the yolk. The thirteen segments of the 

 trunk are more sharply separated from one another, and a lateral 

 constriction slightly deeper than the rest marks the boundary be- 

 tween head and thorax. Both the silk glands and the Malpighian 

 tubules have increased in length. The tracheal invaginations have 

 each sent off tubular branches caudad, cephalad and ventrad. 

 Those directed caudad and cephalad have united with the cor- 

 responding branches in the preceding and succeeding segments to 

 form the longitudinal trunks, while the ventral branches are about 

 to unite with those of the opposite side to form the ventral loops 

 or commissures (TraCom). At this stage the latter are seen 

 on the ventral surface as delicate sharply outlined tubes which as 

 yet have not quite reached the mid-line. 



Stage XII. Estimated at 60 to 62 hours (Fig. XII). The 

 embryo now begins to resemble the larva decidedly in general 



