THE EMBRYOLOGY OF THE HONEY BEE 117 



Moreover, as well be seen by consulting the diagram represented 

 in figure 38 the halves of the protocerebrum are typically directed 

 laterad as well as cephalad. In the larva of the bee the halves 

 of the protocerebrum are, as mentioned above, directed caudad 

 and laterad (Fig. 55). This difference is due to the bending of 

 the anterior end of the germ band and of the resulting embryo 

 around the cephalic pole of the egg and must be constantly kept 

 in mind in comparing the development of the brain of the bee 

 with that of other insects. Those forms in which the development 

 of the brain has been most thoroughly worked out belong princi- 

 pally to the order Orthoptera, and in comparing the embryonic 

 development of the brain of the bee with that of those insects, 

 another important point of difference must be also considered. 

 In the Orthoptera, for example, the development is without the 

 intervention of a larval stage, that is, direct from the embryo to 

 a form completely equipped for active life, and provided, like the 

 mature insect, with functional eyes, antennae and appendages. 

 In the bee, on the other hand, the embryonic development termin- 

 ates in a larva, a form not adapted to an independent existence, 

 and very different structurally from the imago. Many parts of 

 the larva are correspondingly but slightly developed, and may 

 be said to linger in a more or less latent or embryonic condition 

 until near the time of pupation. This is especially true of the 

 brain. At the time of hatching, the brain of the bee is, generally 

 speaking, only comparable to the brain of the embryo of those 

 insects with a direct development. 



The three lobes of the protocerebrum of the insect brain have 

 the following fate, as determined by Viallanes (1891), Wheeler 

 (1893) and Heymons (1895) for the Orthoptera and Dermap- 

 tera. The first (outermost or anterior) forms the optic lobe, 

 the second the optic tract, while the third lobe forms those parts 

 of the imaginal brain included in the protocerebral lobes. On 

 account of its relatively undeveloped condition and the absence of 

 ectodermal thickenings these three divisions of the protocerebrum 

 of the bee are not marked off with the same clearness as in the 

 Orthoptera and Dermaptera, nevertheless three lobes are distin- 

 guishable, both on surface view (Fig. 39) and in longitudinal 

 section (Figs. 43 and 44). The first lobe (iBi\), morphologically 



