THE EMBRYOLOGY OF THE HONEY BEE 175 



specialized, alone displays a developmental feature highly gen- 

 eralized in its nature, since it can hardly be regarded as a new 

 formation. Moreover the rapidity of the development of these 

 tracheal sacs and the brief duration of their external openings 

 make it still more probable that they have escaped the notice of 

 the investigators of the embryology of other insects. Finally, it 

 is a trait of human nature to see only what is looked for, in proof 

 of which it may be said that the discovery of the tracheal invagi- 

 nations of the second maxillary segment in the honey bee .was 

 scarcely more than a happy accident. 



The presence of a pair of tracheal invaginations in the second 

 maxillary segment assists materially to attain a correct concep- 

 tion of the significance of the other invaginations of the cephalic 

 ectoderm. Palmen (1877), Hatschek (1877), Wheeler (1889) 

 and particularly Carriere and Burger (1897) contended for the 

 homology of the silk glands, the tentorial invaginations and the 

 mandibular apodemes with tracheae. According to Carriere and 

 Burger the first pair of tentorial invaginations were to be con- 

 sidered as the first pair of stigmata, the mandibular apodemes the 

 second, the second pair of tentorial invaginations the third, etc. 

 Now that a pair of tracheal sacs is known to exist in the second 

 maxillary segment, the homology of the second pair of tentorial 

 invaginations with the stigmata of the second maxillary segment 

 is completely excluded, and the homology of similar invagina- 

 tions with those of the tracheae is made decidely problematical, 

 especially when one considers that the tracheal invaginations of 

 the second maxillary segment are situated some distance dorsad 

 to the bases of the appendages of that segment. The basis for 

 the conjecture of Janet (i899a, 1900) that the corpora allata 

 furnish material for the tracheae of the head, is likewise removed. 



Aside from the occurrence of a tracheal invagination in the 

 gnathal region, the development of the cheal F> : :em of the 

 honey bee possesses no points of special 'Merest. ..at conforms 

 to the type found in the majority of insects, and th - efore requires 

 no further comment. 



2. Tentorium and Mandibular Apodemes. 



The larval tentorium (Fig. 696) consists of a narrow chitinous 

 bar or central body, compressed in a dorso-ventral direction, 



