No. 398.] CONES IN THE RETINA OF FISHES, HIS 
Pattern 77 is the most complicated found so far. The square 
of pattern F is converted into a rhomb with angles of 60° and 
120°, and a twin cone is added whose axis forms a diagonal 
between the nearer angles of the rhomb. This makes two 
equilateral triangles whose sides are formed by twin cones, and 
whose angles are occupied each by a single cone. This pat- 
tern has been found in Lucius (Figs. 18, 19). 
No suggestion is offered as to the significance of these 
various patterns or the causes that have led to the various 
modifications. 
In several species we have not so far been able to make out 
any regularity or, in fact, the nature of the cones. These are 
the catfishes and Catostomus, one of the suckers. 
resting on the outer limiting membrane (Fig. 1). Below this membrane and 
exactly opposite each cone is a conical nucleus with a diameter less than that of 
the cone. With Biondi-Ehrlich the nuclei are stained a blue purple and the rest 
of the structures pink, so that there is no difficulty in separating parts. The 
single cones differ from the twins in possessing a central deeper staining core in 
the outer segment (Fig. 13). Besides these nuclei there are a few others, more 
spherical and slightly larger, just within the inner ends of this layer of cells — the 
rod nuclei. This inner layer of cells seems most abundant about midway between 
the optic nerve and the ora serrata. There are about two and one-half times as 
many of the outer nuclei as of these inner. 
