32 THE GENETIC AND THE OPERATIVE EVIDENCE 



to a "lower" degree. The difference between dominant and recessive 

 whites rests on the fact that in one case one member of a pair of fac- 

 tors gives white and in the other both members are necessary. But 

 obviously such a distinction is not important, and if it were worth 

 while the case might be argued for recessive whites being also epistatic. 

 The whole tangle goes back to a false interpretation of presence and 

 absence of characters and presence and absence of factors. As I have 

 gone over this ground recently in my paper on the Theory of the Gene, 

 I need not repeat here what I tried to make clear there. 



ENDOCRINE CELLS IN OVARY AND TESTES OF BIRDS. 



The occurence of gland-like cells with an internal secretion in the 

 ovary and testes of fowls has been described by a number of writers 

 and denied, at least for the testes, by others. The work of Boring and 

 Pearl has done much to bring this question to a satisfactory solution, 

 for they have tested out and made use of the best reagents that their 

 predecessors had discovered and have used a much greater amount of 

 material. As they have reviewed very fully the literature of the subject, 

 it will not be necessary to go over the ground again in detail. 



In the follicles of the ovary there are present, according to Boring 

 and Pearl, groups or nests of cells lying among the connective tissue of 

 the inner theca. The cells are about three times as large as the ordi- 

 nary connective-tissue cells of the ovary. The cytoplasm is clear and 

 vacuolated, "only occasionally containing a few acidophile granules 

 which stain with the fuchsin in Mallory's stain or the eosin of Mann's 

 stain, while the real interstitial cells are crowded with granules." 



When the egg is set free from its follicle, the latter collapses and the 

 rupture becomes closed. A mass of cells collects in the center of the 

 collapsed structure which develop yellow pigment. The cells, lying in 

 the puckered edge of the follicle, may also develop such yellow color. 

 The cells that produce the yellow pigment come from the nests of cells 

 that lay originally mainly in the theca interna. Either by migration 

 or by division they come to fill up the central cavity. The yellow 

 substance in the cells is not fat, since it does not dissolve in the clearing 

 oils, nor can it be protein, for it does not take acid stains as normal 

 secretion granules of protein. It does not dissolve in HC1, HN0 3 , 

 or H 2 S0 4 , nor in strong KOH, although the latter turns the pigment a 

 bright red color. Many other substances were also tried by Boring and 

 Pearl, but none of them dissolved the yellow pigment, which reacts 

 in this respect in the same way as does the yellow pigment in the 

 luteal cells of the mammal. The similarity in the nature of the pig- 

 ments in the two cases is an argument in favor of the view that the 

 cells that produce the pigment are the same in both groups. In the 



