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external limiting membrane, so that their outer ends become 
somewhat flattened (fig. 7, nuc . 1>3 ’ 4 ). In tangential sections 
the nuclei of the cones are seen to be connected by a syncytial 
network of protoplasm (fig. 10, syn) formed by the extension 
of the cytoplasmic investment of each. Bernard ( 3 , 4 , 5 ), 
regards the retina as composed not of cells, but of a syncytium 
in which the nuclei are arranged in layers. The cytoplasm 
connecting the nuclei of the cones in Sphenodon certainly 
forms a network, but at the same time the connection of the 
nuclei with the inner segments is so definite that I must agree 
with most writers that the sensory epithelium is a definite 
layer of cells whose nuclei are situated in the outer nuclear 
layer. Each member of one of the so-called double or twin 
cones has a nucleus which does not differ perceptibly in shape 
or size from those of the ordinary single cones (figs. 7, 
nuc , 3,4 ). 
The second kind of nucleus present in the outer nuclear 
layer attracts attention at once. They are rounded and 
arranged in a more or less definite single layer close to the 
junction with the outer molecular layer (figs. 4 and 7, n.d.b.). 
Each is surrounded by a definite space, due doubtless to 
shrinkage, and resembles in appearance the nucleus of one of 
the bipolar cells of the inner nuclear layer (figs. 4, 11, n.b.). 
According to various authors these nuclei are to be regarded 
as belonging to bipolar nerve-cells which have migrated 
from the inner to the outer nuclear layer. Gaupp ( 30 ) figures 
them in the frog’s retina, and calls them “Versprengte 
Bipolare.” I could find no trace of fibrils coming from them, 
even in the preparations which showed fibrils in other parts, 
but owing to the nature of my material this proves nothing 
as to the existence or non-existence of such fibrils. 
The outer nuclear layer is bounded on its outer aspect by 
the membrana limitans externa (figs. 2, 4, 5, 8, etc., m.l.e.), 
appearing in vertical sections as a very definite, darkly stain- 
ing line, and formed according to most authors by the outer 
parts of the Muller’s fibres. 
