TRANSACTIONS OF SECTION D. 669 



was placed witli an inbred white fantai], the other with an extremely vigorous well- 

 matured black barb. In course of time a pure-white bird was reared by the white 

 fantail, and two dark birds by the black barb. Owing probably to the fantail being 

 inbi-ed and the blue-rock being still barely mature, the young white bird died soon 

 after leaving the nest. No birds were hatched from the second and third pairs of eggs 

 laid by the fantail, but from the fourth pair two birds were hatched which are now 

 nearly full-grown. These young birds are of a darker shade of blue, and look 

 larger and more vigorous than their blue-rock sire. As in the Indian variety of 

 the blue-rock pigeon the croup is blue, and, as in some of the Eastern blue-rocks, 

 the wings are slightly chequered. They, however, only essentially difter from their 

 sire in having four extra feathers in the tail. The first pair of birds hatched by 

 the black barb when they reached maturity early iu August might have passed 

 for young barbs with somewhat long beaks. Since the first pair were hatched in 

 March the blue-rock and black barb have reared six other birds. One of the second 

 brood closely resembles the first birds liatched ; the other is of a greyish 

 colour, witli slightly mottled wings, a long beak, and a tail bar. The 

 birds of the third nest are both of a greyish colom*, but have indis- 

 tinct wing bars as well as a tail bar. Of the fourth pair of young one 

 is greyish like the birds of the third nest, the other is of a darlc blue colour with 

 slightly chequered wings, and a head, beak, and bars as in its blue-rock sire. The 

 gradual change from black to dark blue in the blue-rock barb crosses is very 

 remarkable. I can only account for the almost mathematical regularity of the 

 change by supposing it has kept pace with a gradual increase in the vigour or 

 prepotency in the young blue-rock. Eventually the offspring of the blue-rock 

 mated to the black barb, like the offspring of its brother with the white fantail, 

 may be of a slaty blue colour, and otherwise resemble a wild blue-rock pigeon. Many 

 breeders would explain the oti'spring taking more and more after the sire by the 

 doctrine of Saturation — a doctrine that finds much favour amongst breeders — but 

 as identical results were obtained when young females were mated with well- 

 matured males the saturation explanation falls to the ground. 



Like results were obtained by breeding young grey quarter-wild rabbits with 

 fin old white Angora buck : the first young were white, the subsequent young 

 were white, grey, and bluish grey. From these results it follows that, when old 

 and young but slightly different members of a variety or species are mated a 

 wonderfully perfect series of intermediate forms is likely to be produced. Amongst 

 wild animals the young males rarely have a chance of breeding with the young 

 females ; hence amongst wild animals, owing to age being a cause of variation, a 

 considerable amount of material is doubtless constantly provided for selection, 

 thus aff'ording a variety an additional chance of adapting itself to slight 

 fluctuations in the environment, 



In the results obtained by crossing mature, vigorous, and, in some cases, inbred 

 males with barely mature females an explanation may be found why in some 

 families the same features have persisted almost unaltered for many generations ; 

 why in his features the squire of to-day sometimes exactly reproduces the lines of 

 his ancestors, as seen in portraits and monumental brasses. It should, however, 

 be borne in mind that highly prepotent forms are capable from the first of so 

 completely controlling the development that they transmit their peculiar traits to 

 all their off"spring. 



Is Ripeness of the Germ-Cells a Cause of Variation ? 



While difl^erence in age may sometimes account for the earlier broods and 

 litters resembling one of the parents, it fails to account for the very pronounced 

 variation often found in a single brood or litter, and for much of the dissimilarity 

 between members of the same human family. When a sinffle fertilised germ-cell, 

 as occasionally happens, gives rise to twins, they are always identical ; hence it 

 may be assumed differences in members of the same fiimily have their source 

 in difl'erences in the germ-cells from which they spring. If the offspring vary 

 with the maturity of the soma it may also vary with the maturity of the germ- 

 cells, or at leart with their condition at the moruent of conjugation. 



