2/2 FRANK H. PIKE. 



A few numerical results will make these contrasts more evi- 

 dent. There are present in each eye of a normal decapod about 

 2,500 ommatidia. (Parker, '95). Each ommatidium is com- 

 posed of sixteen elements : two corneagen cells, four cone cells, 

 two distal retinula cells, one rudimentary and seven functional 

 proximal retinula cells, and one or more accessory pigment cells. 

 In the retina of a normal eye there are, then, about 40,000 cells, 

 about 22,000 of these being retinula cells. There are in the 

 degenerate eye not more than 100 and not less than co retinula 

 cells, and not more than ten or twelve cone cells. The cone 

 cells in the normal eye outnumber those in the degenerate eye a 

 thousand to one, and the retinula cells of the normal eye outnum- 

 ber those of the degenerate eye by at least two hundred to one. 



As stated above, the ratio of the length of the eye-stalk to its 

 width in the degenerate eye is 1.3. In a normal crayfish eye I 

 found this ratio to be 1.9. In the eye shown in Fig. 4, this ratio 

 is 1.6. I do not know the range of variation in this ratio in the 

 normal eye, but I feel safe in saying that the degenerate eye has 

 decreased relatively more in length than in width. 



THE MINUTE ANATOMY. 



The Retina in tJic Left Eye. The hypodermis consists of 

 oblong cells closely applied to the cuticula and containing relatively 

 large nuclei, Fig. 5. At the extreme tip, the cells become more 

 spherical in shape and are slightly separated from the cuticula. 

 The nuclei are less prominent than in the other hypodermis cells. 

 Beneath these smaller cells is a layer of three somewhat larger 

 spherical cells. Below these occurs a layer of two cells. All 

 have small nuclei and clear cytoplasm. Two irregular masses, 

 staining deeply with haemalum but exhibiting no discoverable 

 structure, lie, one on each side, immediately beneath the hypo- 

 dermis and to one side of the clear cells above mentioned. Im- 

 mediately beneath these dark masses are two other irregular, 

 structureless patches staining diffusely with eosin and not at all 

 with haemalum. 



Miss Seaton ('03 ) states that, in the compound eyes of Machilis, 

 the cone cells do not stain readily with plasma stains. In some 

 of my own preparations, the cone cells do not stain as readily 



