154 THE EMBRYOLOGY OF THE HONEY BEE 



and the ectoderm forming the optic lobe is not folded to any 

 extent, being merely bent inward to form a cup-shaped cavity. 

 At the beginning of the process, the optic plate is connected with 

 the optic lobe by a strand of cells which is said later to constitute 

 the optic nerve. Nothing of this kind was seen in the honey bee. 



In Patten's next paper (1889), on the eyes of the beetle Acilius 

 a long curved slit-like invagination, or rather three such invagina- 

 tions, almost continuous, were described as concerned in the 

 formation of the optic lobe. One of these invaginations was 

 considered as rudimentary. The other two seem together to 

 correspond very closely to the invaginations forming the optic 

 lobes of the bee in their form, situation and relation to the sur- 

 rounding parts. As in the honey bee, the ectoderm destined to 

 form the optic plate lies at first external to the future optic lobe. 



Heider (1889) described a similar condition in Hydrophilus. 

 Heider's text figure 5 representing a transverse section shows 

 an infolding strikingly similar to 586. All the relations are 

 apparently the same as in the honey bee. Moreover the ectoderm 

 from which the optic lobe is formed appears to also consist of a 

 single layer of columnar cells. 



All the cases thus far studied fall broadly into two classes: 

 those in which the optic lobe is formed by delamination, and those 

 in which it is formed by infolding. To the first class belong 

 representatives of the order Orthoptera and the nearly related 

 order Dermaptera. To the second class belong representatives of 

 the Coleoptera and Hymenoptera. In this class the optic plate is 

 formed from ectoderm lying outside of and immediately sur- 

 rounding that destined to form the optic lobes, in other words 

 the optic lobe and optic plate are formed from separate areas 

 of the ectoderm, while in the first class they are formed from the 

 same area. In the first class (Orthoptera, Dermaptera) the optic 

 lobes undergo rather a complex series of changes in order to 

 arrive at their ultimate or imaginal form. The postembryonic 

 changes undergone by the optic lobes in insects belonging to the 

 second class are unknown so that a basis for a definite comparison 

 is lacking, and only a guess is possible as to the meaning of the 

 different parts. A comparison of the optic lobes of the bee at 

 Stage XV with those of Mantis or Xiphidium at a stage shortly 



