62 T. H. MORGAN. 



ever, in the eye on the left side of the figure (47), the continua- 

 tion of the corneal hypodermis with the middle layer is seen, and 

 in the right eye the pigment layer is intimately connected with 

 the hypodermis on the outer side of the eye ; so that the arrange- 

 ment is essentially as in older stages. I could not determine 

 definitely as to the number of cells forming the pigment layer, 

 but in cross-section one can discover not more than two nuclei, 

 so that the number must be exceedingly small. Besides the pair 

 of eyes seen in this figure, there is an anterior pair resembling 

 the above both in structure and size. There is one difference 

 shown in the sections of the anterior eyes, viz. that there is a 

 thickening of hypodermal cells on each side just beyond the 

 outer corner of the eyes, but of this I shall speak later. More- 

 over, the anterior eyes are nearer together than the posterior pair. 



Fig. 46 is from a larva without any walking legs, at an age 

 shown by Fig. XIV, Plate V. The larva has but a single pair 

 of eyes, which correspond to the anterior of the two pairs of older 

 larvse. We find the eyes have essentially the same structure as 

 in the one last described, but are much nearer together than 

 those of the last figure (a posterior pair). Each is composed of 

 three layers. Of these the middle is much larger, and is com- 

 posed of two large transparent cells with large nuclei. The con- 

 tinuity of the corneal hypodermis with the middle layer was not 

 clearly made out, nor that of the pigment layer with the ecto- 

 derm below the eye ; but I think we may fairly push our inter- 

 pretation even to this, but on account of the extreme smallness 

 of the eye and the difficulty of making very thin sections, such 

 connections would not be readily discovered. The posterior 

 layer of the eye seems to be formed of but a single large flat- 

 tened, pigmented cell, showing a clear nucleus, but it cannot be 

 affirmed with anything like certainty that this is the only cell. 



On each side of the anterior eyes the ectoderm, as shown in Fig. 

 46, is a greatly thickened mass, indeed forming two bodies about 

 the size of the two eyes themselves. I am at a loss to interpret 

 these thickenings. At first I believed they might be connected 

 with the sudden increase in the size of the eye, and the very great 

 change in size in the eye between stages XV and XYI of Plate 

 Y might seem to support such an hypothesis. But, on the other 

 hand, the posterior eyes also increase greatly in size at the same 



