THE EYK IN NORMAL AND " EYELESS " DROSOl'H II.A. 247 



became at once evident. Many of the eyes of the eyeless stock 

 were simply reduced in size. Most of these reduced eyes have a 

 large number of ommatidia (Plate II, Fig. 2), but obviously even 

 the larger eyes have a smaller number than have the normal. 

 Some of the eyes, however, are very small, sections through the 

 middle showing scarcely half a dozen ommatidia. Plate III., 

 Figs. 3 to 8 are microphotographs through heads of eyelcs- Hies. 

 In Fig. 3 t here is a small eye on the right side but none on the left. 

 < Mi the right -Me the three optic ganglia are present, for a higher 

 magnification reveals the fact that the middle ganglionic mass 

 here sho\\n is duplex, representing both the median and tin- inner 

 ganglia. I k-. 4 shows a head with a small eye >n each side. < Mi 

 tin- Kit side tin.- outer ganglion is someuhat rounded. ,uM the 

 mass of fibers connecting it to the median ganglion is larger in 

 propni -tii. n than that of the normal eye. Helo\\ tlii- mass "t 

 coimci ting fibers may be seen the median and inner ganglia, each 

 a double Irii like structure as in the normal eye. Tin- section 

 does not go through the optic tract of the right side. I md 



<} -how r.idi a fair-si/ed eye on the right side and aU<> the three 

 :can<lia of the right optic tract. In Fi s r . 5 thr >i-ctii.n . 

 through but a small portion of the brain. \-"\^. ~ shows a -mailer 

 on the right side and all three optic ganglia. ahli<>u.Ji in tin- 

 ]iii nnr the median aiul inner are so close that tl em to t"im 



a Miiije mass. These and other sections >ln.\\ that \\lu-ri- tin- 

 mninatidia are present at all they seem to have the normal 

 structure and all three of the optic ganglia are pn -nit tlu.ndi in 

 man\ cases they are reduced in size corresponding to the -i/< 

 tin 



In the totally eyeless flics, that is, in tln.-e Ilie- th.it -ln.\\ed no 

 i-Mernal ti.ue of ommatidia, the outer ganglion was a No .il.M-nt 

 i Plate II.. 1 ig. 3). This most distal ganglion had disappeared 

 a> had the .> e itself. The other two ganglia, however, were 

 present, though much contracted and in close apposition. This 

 i> \\ell illustrated by the text-figures I to 5 which are outlines of 

 the median and inner ganglia in the totally eyeless condition. 

 These two ganglia have become a rounded, more or less shapeless 

 mass, and it is only with high magnification that the division 

 between them can always be made out. A close study of the 

 ganglia, however, always revealed the fact that the mass is 



