CROSSES OF JAPANESE TURTLE-DOVES WITH BLOND AND WHITE RING-DOVES. 71 



forms examined by the editor indicate that, similar to the orientalis x alba cross, 

 the females are shghtly darker than the males. This situation was not adequately 

 treated by the author, though he has noted that the "juvenal" plumage of the 

 first-hatched female of this series (treated in table 48) was slightly "lighter" in 

 color than her male nest-mate. 



Color and Sex in F^ Ring- Japanese Hybrids: — The very low fertility of the 

 Fi hybrids, and the weakness, short life and sex-abnormalities which are associated 

 with the few gametes which do begin development, have here prevented a full 

 elucidation of the relation of sex and color in the F2 generation. The author's 

 limited data bearing on this point are given in tables 49 to 52. The back-crosses 

 with the parent species are far more fertile than are crosses made inter se. The 

 very restricted life-terms and the varied abnormalities formed from these crosses 

 afford the best of material for the study of many important problems.^ 



RECIPROCAL CROSSES OF ST. ALBA AND T. ORIENTALIS. 



Several of the subjects mentioned in the introductory statement of this chapter 

 can be best examined through a subdivision of the rather extensive breeding data 

 into the four groups into which they can be conveniently classified. Frequent or 

 constant reference to the complete original data as given in the tables will, however, 

 be found quite necessary. 



Orientalis male x alba female. — The very complete breeding record of a male 

 Japanese turtle mated to female white rings is given in tables 37 to 41. This 

 includes 10 years of breeding and 11 years of the life of this particular male. Tests 

 were made with 6 different females. A glance at the data will make it clear that 

 the life-term of the offspring of the resulting hybrids is quite long; longer even than 

 that of the longer-lived parental species when its young are reared in captivity. This 

 we shall later see holds true also for the reciprocal hybrids. 



In this fact of increased longevity in these hybrids one notes that a very 

 important momentum is given to the basic and sustaining powers and processes 

 of the organism by the "mere act of crossing" individuals of these two genera; 

 and, having considered this point, one becomes the better prepared to interpret 

 other unusual features of these data, particularly the data on sex. These 

 latter features are quite probably but another aspect of the same principle 

 which expresses itself in an increased longevity. In other words, the same 

 thing that drives forward the life-term in all of the offspring drives forward also 

 sex-development in all of the offspring. Germs that are not otherwise weakened 

 may be carried by this impulse (increased vigor through a wide cross) to a 

 higher level of sex-development than they would otherwise have attained, namely, 

 to maleness. 



Further examination of the data referred to above will show that the fertility of 

 this cross is remarkably high. In 87 tests (tables 37 to 40) only 4 failed to show 

 some development, while only 1 egg began to develop and stopped short of hatching; 



* The editor is making extensive studies on many subjects connected with the size, chemistry, and stored energy 

 of the egg, and of the relation these bear to sex and fertility; on the relation of season and "crowding" of clutches to 

 sex ; and the question of the relative infertility of these hybrids. The results of these studies must appear later. The 

 additional knowledge obtained from these sources, however, gives the editor confidence concerning some points of 

 the present chapter which do not appear conclusive from the data available for the present volume. 



