618 HOWARD. [VoL. XIX. 
the cones of some animals possess spiral fibers, seems fairly 
certain. \Whether there is both an external straight system 
and an internal spiral one, as maintained by Hesse (: 04), 
is open to question. 
The external straight fibrils in Necturus have been suf- 
ficiently demonstrated. As to the inner dark staining struc- 
ture, since it so frequently resembles a spiral, and since the 
latter is demonstrable in some animals, the balance of evidence 
would perhaps be in favour of the existence of that type of 
structure. That the external fibrils have a mechanical function 
(Hesse, : 04), I think is no more likely than that that should 
be the office of a spiral. The high degree of contractility ia 
the cone would not be inconsistent with a contractile spiral, 
such as is to be seen in the stalk of Vorticella. I have observed 
no sign of spiral fibrils in the inner segment of the cones of 
Necturus or the goldfish, except an occasional slightly oblique 
direction of the peripheral stained fibrils in Necturus. The 
double circle of fibrils, as seen in cross sections of inner seg- 
ments of the cones, may, however, have some special sig- 
nificance, though they are, so far as I have been able to 
determine, all of the same character. 
CG. Dousve Cones. 
The double cones of Necturus, showing the extreme of 
differentiation and evident specialization for particular func- 
tions, may offer a clue as to the functions of the various 
parts of the visual cells, and perhaps indicate the original 
line of differentiation between rods and cones. ‘The far- 
‘cone, with its marked development of fibrils and other char- 
acteristics, practically the same as the single cones, evidently 
functions as these do, while the rear-cone, with its irregular 
and enormously enlarged paraboloid and ellipsoid of dif-— 
ferent form and staining qualities, must have a different office. 
On the theory that the nuclei of cells in general have a 
trophic function, it seems not unlikely that the near-cone 
