276 ANDREWS. [Vol. V. 



round the refracting cells usually, but not in any precise number 

 or positions. 



This formation of the eye from a hemispherical thickening 

 of the epidermis covered by the ordinary thin cuticle, having 

 the cells thickened at the large, peripheral surface, and drawn 

 out into fibre-like processes where crowded at the central part 

 of the eye, as well as the irregular arrangement of the variable 

 number of refracting cells packed in amongst the ordinary pig- 

 ment cells, may be easily seen also in preserved branchiae that 

 are overstained in picro-carmine, depigmented in Grenacher's 

 liquid, and mounted in glycerine. 



It is to be noted, in addition, that the longitudinal bands of 

 cilia found along the branchial stem at the junction of the outer 

 and lateral faces, are interrupted where eyes occur, so that the 

 eye itself is not ciliated : this is shown in transverse sections 

 (Fig. 14). 



In examining fresh, living branchiae, however, I saw, upon one 

 occasion, what appeared to be stiff, seta-like projections from 

 the eye ; but these were then disregarded, as being only appear- 

 ances produced by the adjoining cilia of the branchia. 



To supplement the knowledge of the eye obtained as above, 

 actual sections were resorted to ; these confirm all the above 

 points in the structure of these so-called compound eyes. Lon- 

 gitudinal sections, stained in Kleincnberg's hematoxylin (Fig. 7), 

 show the elongated, epithelial cells proximally, and the short, 

 cuboidal ones distally; the unmodified, thin cuticle over the eye; 

 the oblique, radiating position of the cells that make up the 

 pigmented eye ; the presence of cells with peripheral nuclei, and 

 of those with more centrally placed nuclei ; the occurrence of 

 clear, refracting inclusions, of which the above section happens 

 to show only a very small number, two ; and finally the passage 

 of the elongated, central ends of the cells underneath the proxi- 

 mal epithelium as a band of nerve-processes containing a nucleus 

 here and there, one only shown in this section. 



This nerve may be followed through several transverse sec- 

 tions as a rounded cord of fibrils (Fig. 13) lying imbedded in the 

 epidermis proximal to the eye and at the bases of these cells. 

 Farther down it seems to be resolved into smaller branches, or 

 a network, perhaps, and could not be followed into any direct 

 connection with the two large, longitudinal nerves of the bran- 



