568 HOWARD. [Vov. XIX. 
to no such view, his results were so interpreted by others, 
e. g., Schwalbe. This idea of the cuticular nature of the outer 
segments has met with general acceptance and has remained 
as authoritative almost up to the present day. Thus one finds 
frequently in text-books, where the outer segment alone is 
referred to, such expressions as: “entspricht einer Cuticular- 
bildung” (Schwalbe, ’87, p. 104), and “der Ausdruck einer 
kutikularen Auflagerung” (Rauber, :03, p. 810). Or the 
entire rod, or cone, is called a “Cuticularenbildung” (Wieder- 
sheim, ’86), an ‘“Abscheideproduct” (Gegenbaur, ’98, p. 935). 
From time to time there have appeared in the literature 
on the retina results quite out of the ordinary, whose non- 
acceptance may be attributed to lack of confirmation by others, 
or to obvious insufficiency of evidence. The position, for 
instance, taken by Borysiekiewicz (’87), that rods and cones 
are non-nervous, seems to have received little support. Norris 
and Wallach (’94) describe “Distal connecting loops between 
visual cells.” The photographs which they publish, to illus- 
trate this condition, are certainly not convincing. Johnson 
(95) finds a “branching central fibre” in the visual cell. Pes 
(:00) maintains that the ellipsoid acts as a nucleus. Bernard 
( : 00-03) considers the visual cells to be vesicular projections 
from a syncytial retina. 
The slow advance in the study of the retina since Schultze’s 
time would seem at first sight rather strange in the light of 
recent progress in cytological technique. It might be partially 
accounted for, however, by the fact, that, owing to the extreme 
delicacy and instability of the rods and cones, many recently 
devised neurological methods are inapplicable. 
In noticeable contrast with the condition of the problem 
in vertebrates has been the progress in the study of the ter- 
minal visual organs of invertebrates. In the arthropods, for 
instance, the rhabdomes, which were supposed by earlier writers 
(Hensen, ’65; Grenacher, "79; Watase, ‘90) to have been 
formed by secretions, have been found by later workers to be 
living tissue of marvellous complexity. Schultze (’724), who 
