COMPOUND EYES OF ARTHROPODS. 311 



granular protoplasm and a largo nucleus. At the basal end of 

 each cell there exists an accumulation of transparent liquid sub- 

 stance. Beneath ommatidial area a well defined bascnicMt mem- 

 brane {B. 21), which is the continuation of the same membrane 

 existing under the general ectoderm of the body, sharply marks 

 out the ommatidial structure from the mesodermic tissues. 



In Fig. 58, which is taken' a few sections behind the preceding, 

 is shown the ommatidial area at its widest part. Four omma- 

 tidia formed by the undulating folds of the ectoderm are shown, 

 each depression being accompanied by a corresponding thick- 

 ening" of the chitin, forming the rudiment of the lens-cone (C). 



On both sides of the ommatidial area we find the lateral 

 invagination of the ectoderm. The cells forming the invaginated 

 folds undergo enormous enlargement, and in the basal end of 

 each cell is shown a large accumulation of transparent fluid. 

 The cells forming the inner walls of the dorsal and ventral folds 

 of invaginations undergo various metamorphoses. Each of them 

 becomes divided into a number of smaller cells, each of these 

 segments being packed with extremely lino pigment granules. 

 As the cells in the inner walls of the dorsal and ventral folds 

 ((/./, v.f) become divided up into a number of smaller pigmented 

 segments, they are constantly pushed out towards the surface, 

 where they, grouping themselves into a number of onnnatidia, 

 increase the general surface of the ommatidial area. Thus, 

 the older oramatidia are found in the middle and the younger 

 ommatidia are to be found around the marginal portion of the 

 ocular area. 



In Fig. 59 a section is shown in which the ommatidial area is 

 narrower than the preceding. In Figs. GO and tU this narrowing 

 of the ommatidial portion continues, and in Fig. 62 the dorsal 

 and the ventral folds meet in the median line. In Fig. 63 the 

 median fold becomes completely buried beneath the general 

 ectoderm. In Fig. 6-i the section passes near the posterior 

 extremity of the median fold, where the reduction in the size of 

 the tube as well as its increased distance from the level of the 

 general ectoderm is clearly discernible. 



In all the figures above described Pc/.c means the pigment 

 cells, which in the state of nature are highly pigmented, each 

 with a small eccentric nucleus. Each section has been carefully 



