536 THE SENSES AND SENSORY ORGANS. 
observations, surrounds, but does not cover, the outer ends of 
the retinal rods, which perforate the pigmented tissue and 
terminate in juxtaposition with the membrana basilaris.« If 
these pigment cells are the representatives of the cells, the 
nuclei of which are termed chaplet cells by Viallanes, as I 
believe they are, the latter are clearly not nervous elements in 
the sense in which the term is used by previous writers, 
although the cells in question undoubtedly originate from the 
retinal neuroblast. 
The Palisade Cells of Carriere—These are undoubtedly the 
structures which I describe as the proximal elements of the 
retinule. Carriére describes them as nucleated cells. Hickson 
discovered that the nuclei lie in their sheaths, and this state- 
ment is undoubtedly correct. They contain no nuclei, and 
each consists of a bundle usually of seven fusiform enlarge- 
ments of the fibres of the optic nerve. These elements, which 
I formerly termed fascelli, are surrounded by a sustentacular 
sheath, and each sheath exhibits a single nucleus. The susten- 
tacular sheath is pigmented in Noctuids and consists of thread- 
like fibres similar to the fringes of the retinal pigment cells of 
Vertebrates. 
The Distal Segments of the Bacilli are usually very slender, but 
expand at their outer ends; they are highly refractive, and 
frequently exhibit longitudinal striz in preparations fixed in 
osmium peroxide. They are frequently curved and vacuolated. 
The demonstration of these elements is difficult, but in suc- 
cessful preparations their similarity to the outer segments of 
the rods and cones of vertebrates is most striking, and every- 
one who has worked at the histology of the vertebrate retina 
knows that in many Vertebrates it is by no means easy to 
preserve these structures in a satisfactory manner. 
Like the distal outer segments of the vertebrate retina, these 
structures resist most stains, but they can be coloured with 
diffuse aniline stains; the coloration is, however, usually 
evanescent. Such preparations should be cleared with xylol 
and carbolic acid, as oil of cloves usually removes all traces of 
the stain in a few minutes. 
