FERTILITY AND THE SEXES. 21 



made specially to test this point and to learn somethinia; of the nature and hen^ditary 

 basis of sex. 



"The fertility of the crosses extends to the hybrids, but generally not with the full 

 strength and constancy shown in the parent birds. In this respect, the generic (ring x 

 turtle) hybrids fall more or less below the specific hybrids, and in both classes the degrees 

 in fertility descend with the degrees in relationship between the parent species." .... 

 The hybrids are more often males than females.'* 



" Cierms are as variable as the soma itself. A recent proof of this I find in the young of 

 a pair of homers (Dec-Jan. 1908-9). One of the young has juvenal wing-bars like the 

 stock-dove (weakened), the other has feathers almost white and the bars are obsolete — 

 only traces." (K 12) 



It is clear then that the central feature of the author's extensive hybridization 

 studies — the subject dealt with in this volume — is the demonstration of germs of 

 several grades of genetic non-equivalence and these strung upon a line; concerning 

 which line he has obtained some definite and illuminating information leading to 

 the conclusion that germs subjected to certain procedures are forced to one or 

 another level of hereditary and developmental power. 



In the following summary the author has presented a situation resj^ecting 

 fertility which he had found to be largely typical of many crosses of pigeons, namely, 

 lower fertility in the very first egg or eggs of the season; then a period of high fer- 

 tility, followed by a prolonged period of much reduced fertility or of absolute 

 infertility in late summer or autumn : 



A male mourning-do\e raised in 1897 was mated during the season of 1898 with a 

 ring-dove, but hatched nothing. The same bird was mated in April 1899 with another 

 ring-dove. This pair had egg and young as follows: 



Here three successive pairs of eggs were hatched between June 14 and August 18. 

 The male continued to sit faithfully until the first week in November. He began to sit 



""In Plants, according to Swingle and Webber (1897, p. 388), wideli/ different families never yield hybrids. 

 Distinct genera usually yield no liybiids Piaiinrl ,v;«r/rv- of sunie genus often yield hybrids. Cultivated races, or 

 natural varieties, of same species u(ii(i:ill\ \ irM IinIhi.I^ \ II 



" "See Buffon, vol. 3, j). o, suiiplriiiini , Mi rl.i I i, in i, , i Ins in vol. 1, p. 312. Davenport concludes (Inheritance 



in Poultry, Pulilicatiou of the (':n in .^ic In^liiiii W ,,-.|iiin;l,,n No. 52, 1906, p. 100) that "prepotency is as truly 



iniportMTil HI iiiliriiijiHc :is lioiiiiiiiiicr 'lliis i> I iiiMiiily true in pigeons. The same author finds also that "the 

 proportinii III ilir u\n ~i \i •, III li\ In iil> i> ii.iiniiil, AiiHiiifz: pigeon hybrids this does not hold." (K 12) 



'' 'I'lii- -I riiinl h^i I- :nlili il l,\ I In . ilii.ir I Inn I ilir :iuihni's data, for comp.ari.son. This record is complete in table 100. 

 Only males are known lioni cicis.-cs ol ilie muurning-dcn e and the ring-dove (a cro,ss of .subfamily rank). 



