494 



SLONAKER. 



Fig. 21. Chicken (Gallus domesticus), left eye, \. N, nerve entrance ; P, 

 pecten. 



Fig. 22. Diagrammatic representation of the comparative thickness of the layers 

 of the retina in the different vertebrates. Measurements were taken of the retina 

 at corresponding positions and magnified 130 diameters, i. Nerve-fibre layer; 

 2. Nerve-cell layer ; 3. Inner molecular layer ; 4. Inner nuclear layer ; 5. Outer 

 molecular layer ; 6. Outer nuclear layer ; 7. Rod and cone layer ; 8. Pigment 

 layer. The last two layers generally overlap. I. Human. II. Cat (Felis catus 

 domesticus). III. Blue Jay (Cyanocitta cristata). IV. Snake (Eutainia sirtalis). 

 V. Frog (Rana catesbiana). VI. Pickerel (Esox reticulatus). 



Fig. 23. Black-Crowned Night Heron (Nycticorax nycticorax), left eye, \. 

 N, nerve entrance ; P, pecten ; AF, area and fovea. 



