556 William Patten 



capped by a thick layer of transparent, and perfectly homogeneous 

 cuticula. The inner, membranous prolongations consist of flatteued, and 

 longitudinally striated bacilli, which end abruptly in three or four 

 short, root-like fibres. The expanded pigmented ends, as far as the 

 base of the nucleus, form a broad collar for the retinophorae (fig. 59). 



The inner circle of cover cells consists of four wedge-shaped, and 

 deeply pigmented cells, covering the two inner thirds of the retino- 

 phorae ; they are widest and thickest at the outer limit of the pigment. 

 There, the outer edges are bevelled, and rapidly decrease in thickness 

 toaverythin, structureless membrane, continuedas far as the outer 

 extremity of the rods. The membranous prolongations of these four 

 cells unite to form a delicate s h e a t h surrounding the outer portion of the 

 retinophorae, between them and the external cover cells, thus indicating 

 that the cells. to which these membranes belong, are more intimately 

 connected with the retinophorae than the outer row of pigment cells 

 (fig. 59 rt. s.). The proximal ends of the four inner cells are narrowed 

 nearly to a point. The outer cells are so arranged that their narrow, 

 basal portions cover the line of contact of the adjacent, inner cells. The 

 oval nuclei of the latter are situated in the middle of the cells, and thickly 

 surrounded with pigment, so that they are seldom seen, except on cross 

 sections. They stain deeply, and with a dullness which is in marked 

 contract with the lighter, but clear and sharp stain characteristic of the 

 nuclei of the retinophorae. 



Since the whole ommatidium is simply a highly specialized por- 

 tion of the hypodermis , we should expect to find the same method 

 of nerve endings there, as in the less modified portions. On sections 

 of the eye, it is hardly possible to observe more than the passage of 

 nerve fibres through the basal membrane, and along the cells to- 

 wards the surface. Isolation of the cells by maceration, according to 

 the methods described below, furnishes the best results. Unfortunately 

 I was not able to obtain perfect control of the process. and the results 

 often varied, especially as far as a complete and rapid Isolation of the 

 cells was concerned ; for sometimes only 24 hours maceration in bichro- 

 mate of potassium, 2%, disassociated the cells completely, and, at the 

 same time, in a remarkably perfect and normal condition, a result 

 which, at other times, was only imperfectly effected after prolonged 

 maceration, and after many important characteristics of the cells had 

 been destroyed. I am inclined to believe that it depends on the physical 

 condition of the animals experimeuted with ; perfectly healthy and fresh 

 ones being more difficult to treat than those which have become weaken- 



