INFLUENX'E OF SPERMATOZOA ON RATE OF DEVELOPMENT OF EMBRYO. 205 



when the passenger male was crossed with ring-dove females. This pigeon has the 

 shortest incubation period known among doves and pigeons. The period is here a 

 little less than 13 days; it averages about 12V days (see table 187). This is a shorter 

 period than that of the ring-dove, in which, as we have seen, the i^eriod is 14 to 15 

 days. The passenger-pigeon's incubation time is nearly as much short of that of 

 the ring-dove as the period of the latter is short of the common pigeon. What is 

 the effect on the incubation time of uniting the male passenger-pigeon and the 

 female ring-dove ? The answer from our data is as follows : For the first egg the 

 period is 14 days plus 20 hours; for the second 13 days i^lus 6 to 20 hours (see tables 

 188 and 189). These figures come close to the normal range for the ring-dove; 

 still I can not help feeling that there is some influence, however small, exercised 

 by the male on the rate of development. Comparing the results obtained with the 

 passenger-pigeon and the common pigeon, when each of these mated to the ring- 

 dove, we find these give us the two extremes. In a condensed form these two crosses 

 may be stated to stand as follows: Common pigeon male x ring-dove female: 

 first egg, 15 days plus; second egg, 14 days plus. Passenger-pigeon male x ring 

 dove female : first egg, 14 days plus 20 hours; second egg, 13 days plus 6 to 20 hours. 

 Females of the same species {St. risoria) are used in both cases; different males are 

 given. One of these males represents an incubation period of about 12.} days, 

 the other a i)eriod of 17 to 18 days. The difference in the result is small, but it is 

 enough to indicate that there is a small though measurable influence of the male 

 on the rate of development. (A more complete summary of these crosses of ring 

 with domestic and passenger-pigeons is given in table 190. — Editor.) 



The red ring-dove of Japan {Streptopelia humilis) has also a short incubation 

 period. This dove, too, has been crossed with the ring-dove, with the result made 

 clear by table 191. The males of this species, too, shortened the period of develop- 

 ment in the egg of the ring by from 12 to 24 hours. The three incubations bearing 

 on this point were made simultaneously.'' 



The effect"' of the sperm of one species on the rate of development of the eggs of 

 another species was observed in many isolated instances with several different 

 crosses. Some of these have been referred to in connection with the tabulated 

 breeding records. Two cases may be added here. 



In the cross of the female wood-pigeon {Columbu palumbus) with a male common 

 pigeon "about one day" was added to the incubation jjeriod; this was found in two 

 cases. (A 14) Another series of matings supplied data for a reciprocal cross. In a 

 female Columba guinea, whose normal period is 16 days plus 12 hours for the flrst 

 egg and 15 days plus 16 to 18 hours (XS 3) for the second, the period became 17 

 days plus 12 hours for the first egg when mated with a C. do7nestica. In the reverse 

 cross a male C. guinea shortened by 1} days the time of hatching of an egg of a 

 homer, the period becoming 16 days plus 20 to 22 hours. "This time is li days 

 shorter than in homers and common pigeons and again is a proof that the male 

 influences the rate or speed of development. "'' (G 3) 



' Nearly all of the data for the preceding parts of this manuscript were obtained from original data catalogued 

 as A HI, A 15, A 10, and R 18. — Editor. 



' The concluding paragraphs were written by the editor. 



^ There is reason to believe that there are many phenomena of inheritance in hybrids — particularly the differ- 

 ences of reciprocal hybrids — which will, at some time, be found to be based essentially upon the "different rates of 

 development" of the forms crossed. If so, such phenomena should perhaps be more easily discovered and analyzed 

 in crosses of annual with biennial plants; but they are probably also discoverable in animal crosses. — Editor. 



