CERTAIN CROSSINGS OF JAPANESE DOVES. 29 



Enough is known of the history, nature, and causation of these deviations or 

 "mutations," some of which have been shown to "breed true," to enable one 

 to predict that they will arise only or almost exclusively from such weakened germs. 



FERTILITY AND LONGEVITY IN PURE-BRED JAPANESE TURTLE-DOVES. 



It remains to indicate the normal percentage of fertile eggs produced by T. 

 orientalis when pairs of individuals of this S]3ecies are mated together, and further, 

 to supply data upon the sex and longevity of the offspring of these matings for 

 comparison with the very limited life-terms noted particularly in crosses of this 

 species with a distantly related one. 



The presentation of the data in a complete and tabulated form will, moreover, 

 serve two other necessary objects. First, these tables assist, as do others of this 

 book, in a demonstration of the relation that exists between season of hatching 

 and of longevity of the offspring, and the further facts of individual differences in 

 the capacity of parents, due to age, health, overwork, etc., to produce strong germs. 

 In the second place, manj^ of the young whose origin is given in these tables are 

 later studied extensively as parents; the all-important features of the germinal 

 foundations from which they grew can be shown adequately, owing to the asso- 

 ciations just noted, only by means of such tabulations. This holds especially true 

 of the "mutations" which appear at the extreme end of the record; and these 

 "mutations" become the subject-matter of the succeeding chapter. 



The one breeding record available for T. turtiir is presented at this point. It 

 much resembles the records for orientalis which are to follow. Table 16 shows that 

 of 9 eggs tested, 8 were hatched; there is no definite record for the other one. The 

 shortest life-term is 4 months, and one of the young was alive and breeding at 

 51 months. The two longest-hved birds were from the second clutch of the season; 

 the egg that probably failed to hatch, and the bird of shortest life-term, were from 

 the last (fifth) clutch of the year, laid July 26-28; 3 males and 4 females are known 

 from this family. 



Especially complete records are available for the results of 4 of 5 matings in 

 pure Japanese turtle-doves.'' From pair 1 there were 21 tests, and, as is shown in 

 table 17, all were hatched; 2 eggs, the first pair of the second season, were poorly 

 incubated, but both developed to hatching. Here again the young of longest 

 life-term arose from early (not the "very earliest") eggs of the season; the birds 

 from the last eggs died youngest. Neither the question of age nor of possible 

 relationship of the two birds of pair 1 can be definitely answered; they were im- 

 ported together and their short-lived offspring may be inbreds. That the term of 

 life of their off .spring is too short — is indeed a "time fuse" set at about 3 months — 

 is apparent. The death of both the parents early in 1906 and the lameness of the 

 sire indicate weakness and possibly old age as contributory causes of their weakened 

 germs. 4 males and 4 females are known from this family. 



The data for pair 2 are very incomplete (table 18). Eggs were obtained only 

 from an unfavorable season of the year. The parents were imported together and 

 may have been related. They were overworked. of their 11 eggs were deserted, 

 for 1 there is no record; probably 3 eggs produced embryos and 1 showed no 

 development. Both parents died soon after these eggs were produced. 



5 Matings involving inbreeding of Japanese turtles are specially considered in the next chapter. 



