CHAPTER VIII. 



GUINEA-PIGEONS CROSSED WITH COMMON PIGEONS. 



The results of crossing the male guinea-pigeon {Columba c/uinea)^ with female 

 homers and domestic doves (and with their hybrids) bring into relief several of the 

 most interesting phenomena of hybridization: (1) the shortened life-term of the 

 hybrid (in so7m crosses); (2) the lesser compatibility of sperm with the ova of 

 hj'brids than with ova from a pure strain; (3) the difference in developmental 

 strength of the germs of individuals of the same strain; (4) the lesser strength of 

 germs produced "out of season" or late in the season; (5) the quantitative nature 

 and basis of fertility; and (6) the power of the sperm of one species to affect the 

 rate of development- of the ova of another species. All of the author's data and 

 observations on these points are given in connection with the several tables. The 

 following textual statements and the summaries are made by the editor. 



The detailed histories of two of these matings, each extending o-\-er a period of 5 

 years, are given in full in tables 63, 64, and 65. The two male guinc^a-iiigcons 

 used in the matings are designated G 1 and G 2. It \\\\\ be oliser\'ed in the tallies 

 just cited that G 1 was mated to 4 different females, and (/ .? to (i different females; 

 also that they were mated to birds of similar constitution, and that finally both 

 males w^ere tested with the same individual female. 



We shall analyze these data rather more fully than is done in most cases else- 

 where in this volume, partlj^ because this treatment may assist the reader not only 

 at this point but at others where a minimum of analysis is given, partly because 

 the data here are very complete and unequivocal, and again because some com- 

 parisons of the results of one of the series of crosses with the other series might 

 otherwise be overlooked. 



The birds concerned in these crosses are of the same genus (see the preceding 

 note), but are very different and probably rather distantly related species. In 

 accord with this the percentage of "infertile" eggs — /. e., eggs capable of little or no 

 development — is high. But the general level of infertility is probably not equally 

 high in the two scries. For male G 1 this percentage is 56, or 24 of 43 tests.'' For 

 G 2 this percentage of infertility is 43, or 15 of 35 tests.-* In partial explanation of 

 this difference, however, the fact that male G 1 and consorts produced a total of 

 56 eggs to only 39 in the other series (overwork) is a matter to be considered. The 

 unequal number of eggs produced during the "out season" would also probably 

 serve to explain still another part of this apparent difference. Nevertheless, male 

 G 1 shows, in 3 of the 4 matings which are A\holly comparable with the 5 matings 

 of male G 2, & smaller percentage of eggs capable of beginning development {G 2 x 



' "Salvador! (p. 241) states that he feels 'sure that the numerous species of Cohimha ought to be arranged in 

 several subgenera.' " (See pi. 80, Vol. I.) 



2 "This time (for eggs of homer fertilized by C. guinea) is IJ days shorter than in liomers and domestic pigeons, 

 and is again a proof that the male influences the rate or .speed of develoimicnt " (P3). The subject is treated in 

 Chap. XVI. — Editor. 



' 11 eggs with "no record," but probably nearly all of mi <lcv('liipniciil , ari' not included; this makes the figure 

 55 per cent too low. 



'Only 2 cases of "no record, probably no developniriit ," ami rliiuinalini; tlic mating of sire to daughter, not 

 represented in matings oi G 1. 



