SPERMATOGENESIS OF THE CHICKEN 55 



color patterns in crosses of game bantams. Davenport ('11 and 

 '12) reports the same sort of results for color pattern inheritance 

 in Dark Brahma X Brown Leghorn crosses. Sturtevant ('11 

 and '12) in crosses of Brown Leghorn and Columbian Wyandottes 

 finds the female heterozygous for sex and certain sex-linked pat- 

 terns and color factors. One of the present writers (Pearl '12) 

 has shown that the factor on which high fecundity depends is 

 sex-linked in the same manner as the barred color pattern (Barred 

 Plymouth Rock and Cornish Indian Game breeds) . 



All of these cases, which cover a wide range of the different 

 known types of domesticated Gallus, and include a considerable 

 number of different hereditary characters, agree in showing that 

 the female fowl is heterozygous for sex and sex-linked factors, 

 while the male is homozygous. But Guj^er's (loc. cit) inter- 

 pretation of his cytological observations is flatly opposed to this 

 body of clear-cut and definite evidence, based literalh^ on thou- 

 sands of cases and undergoing continued confirmation in several 

 laboratories in the course of routine breeding operations prima- 

 rilj' carried on for other purposes. As has been seen a number of 

 independent investigations have checked, repeated and extended 

 the experimental work with fowls, always with accordant and 

 mutually confirmatory results. 



Nor is this all. There is a considerable body of definite ex- 

 perimental evidence indicating that in other birds than Gallus 

 the female is the heterozygous and the male the homozygous 

 form. Here we have the investigations of Durham and Marryat 

 ('08) with canaries, those of Staples-Brown ('12), Cole ('12) and 

 Strong^ ('12 a and b) with pigeons, and those of Goodale ('11) 

 with ducks. 



2 Strong's results are included here for the following reasons: (a) his experi- 

 mental facts appear to be in no essential particular different from those of other 

 students of sex-linked inheritance in the pigeon; (b) a simple and direct interpre- 

 tation of his results, in line with other cases of sex-linked inheritance, has been 

 given by Bridges ('13) ; (c) because we are entirely unable to see the logical force 

 of Strong's own interpretation, which makes the male heterozygous. Specifi- 

 cally it seems to violate that fundamental logical principle, which, as most ade- 

 quately stated by Sir William Hamilton, runs: "neither more, nor more onerous, 

 causes are to be assumed, than are necessary to account for the phenomena." 



