RETINA OF LATERAL EYES OF SPHENODON PUNCTATUS. 321 
their small size, have much the same structure as the ones 
described above. Their nuclei (fig. 8, mtc. 2 ), however, as 
mentioned before, are quite distinct in shape and position 
from those of all the other cones. Fig. 8 shows two of 
these small cones. The larger one (c) has a well formed oil 
globule, ellipsoid, and paraboloid. The smaller ( d ) shows 
the ellipsoid, but neither oil globule nor paraboloid, which 
have probably been missed owing to the plane of section. 1 
These small cones may possibly be young ones which are 
thrusting themselves up between the old ones, but there is 
no evidence to show how new sense-cells really originate. 
In this connection I may point out that, according to 
Bernard (2), the cones in other forms are merely stages in 
the development of the rods. 
(3) The Double Cones (figs. 3, 5, 7, 9). 
The so-called double or twin cones are paired structures, each 
pair consisting of a large “near cone” and a small “far cone,” 
always found in conjunction with one another. Both “ near ” 
and “far” cones differ considerably in size, shape and minute 
structure, not only from the ordinary and small single cones 
but also from one another. Double cones are much less 
numerous than the ordinary single cones, there being* about 
half the number over a given area. 
In a paper published in 1900, Eigenmann and Shafer ( 13 ) 
point out that in many fishes distinct patterns are found by 
the arrangement of the double and single cones. Certain 
arrangements of these cones are apparent in the retina of 
Sphenodon, notably liorse-slioes of single cones arranged 
round a double one (fig. 9, j). This pattern is present in 
many parts of the retina, but so many other apparently 
irregular arrangements occur also that one cannot say that 
the cones are arranged on any definite mosaic in this case. 
(a) The near cone (figs. 5, 7, and 8,N.C.) is very much 
larger than the ordinary single cone, the difference in size 
1 The outer segment also is not shown in either case. 
