THB OCELLI. 89 



compact layer of cells, and the protodennic layer is distinctly 

 divided into hexagonal facets. 



Sometimes all these changes apparently take place a day 

 earlier ; but this is partly due to the change of colour in the 

 larval skin taking place much earlier in some cases than in 

 others. The imaginal discs are frequently unfolded to a 

 considerable extent before the pupa case is formed. All the 

 changes in the pupa are much affected by temperature, and I 

 believe they are accelerated by heat. 



Section XIII. The Ocelli. 

 PLATE VIIL, Fio. 8 & 9. 



The Ocelli are three in number ; they are situated in the 

 frontal region, close to the bend in the occipito-frontal plate. 

 The three cornese have not their axes in the same direction ; 

 but are situated on the sides of a small eminence, so that 

 their axes are divergent. Nevertheless they can all be seen 

 from above, so that a simultaneous picture is probably formed 

 on the three retina3, in certain positions, although not upon 

 corresponding portions in all the ocelli. 



The cornese of the ocelli vary in diameter, from 1 -200th to 

 1 -400th of an inch. They are smaller in the males than in the 

 females, differing in this respect from the compound eyes. 

 They are very convex, the inner curve being slightly greater than 

 the outer, and their thickness varies, from 1 -400th to l-600th 

 of an inch. In the adult insect the protoderm is not easily 



