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THE AMERICAN NATURALIST [Vol. XL 



represents the last product of the (Hvision of the germinal nuclei. 

 In fact, division among them docs not wholly cease until the rods 

 of their immediate neighbors have attained a high degree of 

 development. Thus the rod nuclei are the youngest in the retina. 

 All measure 4.3S n in diameter, which is the regular size of the 

 germinal nuclei after the hrst half of the first period of growth. 

 The^ sulfei nodinunutH.ii in M/e uitli the .lc\ clopmcnt of t lie rods 



