124 PROCEEDINGS OF THE ACADEMY OF [Feb., 



tidia in each eye make the preparation of sections an easier matter, 

 since it was not necessary to cut so many eyes. 



The adult ommatidium of the bee was briefly described and figured 

 by Grcnachcr in his celebrated work, Sehorgan der Arthropoden (1879), 

 and has been figured in works on apiculture, but has never been fully 

 worked out in the adult condition, and no work has been done on the 

 development of the eye. Biitschli (1860) in his work on the embryol- 

 ogy of the bee discusses the formation of the eye, but does not go into 

 the subject of the development of the ommatidium. 



This work was taken up with a view to getting, first of all, a complete 

 description of the development and structure, and in addition to get 

 some light on certain problems which are of especial interest from a 

 theoretical standpoint. The innervation of the ommatidium, the 

 method of formation and fundamental plan of the ommatidium, the 

 method of modification of numerical plan and structure in the evolu- 

 tion, the arrangement of ommatidia, the homology of various cells 

 in different ommatidia, and the comparison of ommatidia with other 

 sense-organs are questions which have been much discussed, and in 

 this work an effort has been made to apply the observations made to 

 the solution of these problems. This is done not without the realization 

 that some of these things can be settled only from wide comparisons, 

 but with the thought that a piece of work which takes in the whole 

 course of development is of more value than superficial observations 

 of a large number of forms. Some of the theories are merely matters 

 of interpretation rather than of direct observation, and must remain 

 so until decisive observations are made, but in matters of this kind the 

 accumulation of evidence is of decided value. 



The formation of the optic lobes and the course of the nervous ele- 

 ments through them are problems which have not been taken up for 

 investigation in this work. Kenyon has worked out the structure of 

 the optic lobes for Apis in detail with nerve methods. The technique 

 used in the present work not being suitable for the tracing of nerves, 

 only on matters concerning the nerve endings of the retinula has any 

 investigation been made in this work, and that was not done by 

 Kenyon. 



In the matter of nomenclature an effort has been made to avoid the 

 use of new names or of some of the names which have been proposed 

 by some workers who have special theories to uphold, such as calyx, 

 lentigen, corneagen, etc. In the case of the cells which surround the 

 cone- I have used the name corneal pigment cells, since they have a 

 double function. In other cases I have used generally accepted names. 



