authors' abstract of this paper issued 
bt the bibliographic service, december 6 
STUDIES ON THE RETINA 
THE STRUCTURE OF THE RETINA OF ALLIGATOR MISSISSIPPIENSIS 
AND ITS PHOTOMECHANICAL CHANGES 
HENRY LAURENS AND S. R. DEl^^LER 
Osborn Zoological Laboratory, and the Anatomical Laboratory, School of Medicine,- 
Yale University 
THIRTEEN FIGURES 
INTRODUCTION 
Owing to the variation in kind and distribution of the visual 
cells, the reptilian retina offers an interesting field of investi- 
gation in structure and function, with particular reference to 
the probable functions of the rods and cones under diurnal and 
nocturnal conditions (duplicity theory). Detwiler ('16) studied 
the structure and photomechanical changes in the retina of a 
number of turtles and of lizards, and with the idea of making 
another contribution to our knowledge of the conditions holding 
in the reptiles the present investigation was undertaken. The 
work was started in the spring of 1917, but was necessarily 
abandoned, and only recently has it been possible to resume it. 
The literature on the crocodilian eye is small and rather 
unsatisfactory. Heinemann ('77), in a study of the eyes of 
Mexican reptiles, described the visual cells of Crocodilus rhom- 
bifer cuv. as consisting of characteristic rods alternating with 
considerably fewer and shorter cones. In addition to the typical 
rods he found a much less numerous kind, with yqvj long outer 
segments of platelet structure. The cones are described as 
being also of two kinds, thick and slender, neither of which 
contain colored oil drops, and which occur singly and together 
to form double cones. There is an ellipsoid with a small central 
body in the peripheral portion of the inner segment of both and 
207 
