108 THE EMBRYOLOGY OF THE HONEY BEE 



Viallanes and others have shown. Following the three segments 

 of the primary head division come three, or possibly four seg- 

 ments which enter into the composition of the head of the adult 

 insect and which bear those appendages commonly known as the 

 mouth parts (mandibles and maxillae). The next three segments, 

 bearing legs, form the thorax. The remainder, twelve in number 

 in primitive insects (Heymons, 1895a), of which only eleven are 

 apparent in the majority of the embryos of pterygote insects, as in 

 the honey bee, form the abdomen. 



The early appearance of the definitive segments of the honey 

 bee has already been described, but the precise identification of 

 these is uncertain, even at Stage VII, since the segments of the 

 primary head division are not clearly demarcated, and distinguish- 

 ing characters, in the form of embryonic rudiments, are yet entire- 

 ly lacking. At the Stage following (VIII), all of the segments, 

 excepting the terminal segments of the abdomen, are readily dis- 

 tinguishable and may now be identified, since the rudiments of the 

 appendages, and of the silk glands and spiracles have put in an 

 appearance. The protocerebral and deutocerebral segments (iBr, 

 2Br) are plainly distinguishable, in fact more so than at any other 

 time in the development. The protocerebral segment consists, as 

 already described, of two large lobes extending half way down 

 the sides of the egg, and rounded at their external margins. This 

 segment possesses no recognizable appendages, although certain 

 investigators have compared the labrum (Lm) which in many 

 insects is more or less bilobed, with a pair of fused appendages. 

 Heymons (1895), however, has pointed out that true appendages 

 arise laterad of the nervous system, while the labrum in all cases 

 arises in the mid-line between the two lateral halves of the ner- 

 vous system ; its homology with a pair of fused appendages there- 

 fore seems very improbable. The protocerebral segment, in 

 addition to the labrum, bears the compound eyes and the ocelli, 

 and contains a certain amount of mesoderm, but no coelomic sacs. 

 The deutocerebral segment (2Br) consists also of two large 

 lobes. These are somewhat triangular in outline, and their ex- 

 ternal apices, which are, with respect to the germ band, directed 

 laterad and somewhat caudad, bear the papillate antennal rudi- 

 ments. In certain insects the antennae are post-oral in position 

 at the time of first appearance, and in fact, in the honey bee a 



