506 S. R. DETWILER AND HENRY LAURENS 
The character of the connections of the visual cells with the 
internal nuclear layer could not be determined. In preparations 
stained with Held’s molybdic acid haematoxylin, the internal 
prolongation of the rod nuclei could be followed for a considerable 
distance, but its final connection could not be seen. 
With the establishment of the character of the centripetal con- 
nections of the visual cells which remains to be brought out by 
impregnation or other methods, in addition to observations on 
the functional behavior prior to the period when typical rods 
first appear, more light may be thrown upon the identity of the 
developing visual cells in Amphibia. 
SUMMARY 
1. The fully differentiated retina of Amblystoma punctatum 
possesses characteristic rods and cones (fig. 11). 
2. The initial stage in the development of the visual cell is the 
production of a protoplasmic bud and a clear achromatic globule 
from the cells of the external nuclear layer (fig. 2). The globule, 
which becomes the paraboloid of the inner segment, appears to 
be of cytoplasmic origin, and not of nuclear, as asserted by 
Cameron. 
3. In early stages of the development of the visual cells (eleven 
to thirteen days after tail-bud stage) masses of deeply staining 
granules are seen in iron-haematoxylin preparations (figs. 2 and 
3). These granules contribute mainly to the formation of the 
ellipsoid of the inner segment and to the granular material of the 
outer segment. There is no evidence from our preparations 
which indicates that they are products of pigment ingested from 
the epithelial layer. They may represent transformation pro- 
ducts of mitochondria. 
4. In these early stages the visual cells are all cone-like (figs. 
2 and 3), agreeing in this respect with the conditions characteris- 
tic of the developing amphibian retina (Cameron and Bernard). 
Rod and cone identity based on the position of the diplosome 
such as has been described by Fiirst, Leboucq, and Seefelder has 
not been demonstrated. Rods and cones are later differentiated 
from the primitive, non-specialized visual cells. 
