March 12, 1897.] 



SCIENCE. 



429 



nuclei which are much flattened. The 

 retina is composed of nerve fibres and a 

 single cell layer embracing two kinds of 

 cells : viz. (a) pigment cells and (6) sen- 

 sory cells. In sections along the chief axis 

 of the eye the retina presents three concen- 

 tric zones; the innermost, of a pale yellow- 

 ish color, is composed of the so-called cones; 

 the middle is the pigment zone and exhibits 

 higher radial bands alternating with broader 

 masses of more opaque appearance ; ' the 

 outer zone, which is destitute of pigment 

 contains, nuclei of two kinds : large, pale, 

 circular ones, and smaller, elongated, deeply 

 staining ones. The branches of the optic 

 nerve constitute the outermost portion of 

 this clear zone next to the sclerotic. 



These three zones are really made up of 

 a single layer of cells, the retinal cells, of 

 which there are two kinds : the unpig- 

 mented, or sensory, and the pigmented. The 

 pigment cells are club-shaped and contain 

 granules of dark brown pigment. Their 

 central ends all terminate at nearly the 

 same level and rather abruptlj\ Their 

 basal ends run out into long fibres which 

 are often branched. The lighter radial 

 bands of the middle zone are produced by 

 the sensory cells. These extend nearer to 

 the center of the eye than the pigment 

 cells, each ending in a club-shaped portion 

 that is rounded at its free extremitj'. This 

 club-shaped prolongation is surrounded by 

 a thick mantle of substance having a radi- 

 ally fibrous structure. These prolongations 

 with their mantles constitute the 'cones.' 

 The unpigmented, or sensory, cell itself 

 shows throughout its whole course a longi- 

 tudinally fibrous structure, contains no pig- 

 ment and terminates at its deep end in a 

 large number of fibrous branches. 



The sensory and pigment cells are defi- 

 nitely grouped into sets. Each set, or om- 

 matidium, comprises a single central sen- 

 sory cell and a small number (5-7) of pig- 

 ment cells surrounding it. 



In front of the pigment cells of the antero- 

 ventral margin of the chief eye its sclerotic 

 capsule is somewhat enlarged so as to in- 

 clude a hitherto undescribed structure, 

 which reproduces on a smaller scale almost 

 exactly the conditions found in the chief 

 eye. In one respect only does it differ 

 from the chief eye ; the cells corresponding 

 to the pigment cells of the retina contain 

 no ])igment granules. In other respects it 

 presents the same histological conditions 

 and a similar arrangement of the • histolog- 

 ical elements. The innervation of this ac- 

 cessory retina is effected by nerve fibres 

 from the optic nerve, which accompany 

 those distributed to the antero-ventral por- 

 tion of the chief eye. The cells composing 

 the accessory eye are separated from the 

 pigment cells of the adjacent parts of the 

 chief eye by elongated cells with small oval 

 nuclei. At the angle formed by the juxta- 

 position of the two retinas are seen several 

 very large nuclei. Some of these are prob- 

 ably the nuclei of sensory cells, but there 

 are others which are much larger than the 

 nuclei of the sensory cells and do not seem 

 to be connected with cells terminating in 

 fibrous cones ; they have a striking re- 

 semblance to the large ganglionic cells of 

 the central nervous system. These are 

 the largest nuclei found within the eye cap- 

 sule. 



ITie Optic Lobes of the Bee's Brain. F. C. 



Kenyon. 



In the optic lobes of the bee's brain there 

 are, as in other hexapods, three masses of 

 fibrillar substance surrounded more or less 

 completely by masses of cells. The middle 

 and inner masses or bodies may in section 

 be recognized as composed of a pair of len- 

 ticular, densely and finely fibrillar bodies or 

 capsules, fitted one within the other and 

 with their convex surfaces directed outward, 

 their concave surfaces inward. The cap- 

 sules in each body are sepai-ated from one 



