634 



THE AMERICAN NATURALIST [Vol. XL 



21. Active growth is restricted to the margins of the pigment 

 layers and continues as long as the eye increases in size. 



22. Nuclei of this layer are always of the same size as those 

 found in the early undifferentiated condition. 



23. Pigment granules first form on the side of the layer away 

 from the retina and in the protoplasm between the nuclei. 



24. These granules are never normally found outside the cyto- 

 plasm of the pigment cell. 



25. There is no evidence that pigment is a food substance. 



26. The numerous large blood vessels always present in the 

 choroid coat next the pigment layer may furnish the nutritive 

 material for the development of the retina. 



27. The outer nuclear layer represents the last two genera- 

 tions from the division of the germinal nuclei. 



28. The rod nuclei are the youngest in the retina. 



29. They are more numerous than the cone nuclei, and divi- 

 sion among them does not wholly cease until the rods of their 

 immediate neighbors have attained a high degree of development. 



30. The rods and cones have their|origin in undifferentiated 



31. There is no evidence that any part of the rod or cone is of 

 nuclear origin. 



^ 32. The nuclei of the ro Is and cones retain their caily posi- 



tend to become protruded to varyinii- (Icorces hevond it. as lias 

 been recorded for other animals. 



33. In the development of the retina tliere is no fixed time for 

 the appearance of the different elements. 



