192 ORTHOGENETIC EVOLUTION IN PIGEONS. 



other. Here, if anywhere, we should expect to see the mutationist triumphant. His 

 biometric curves would surely declare gaps in abundance beyond the span of any 

 conceivable bridges. Just as surely is he a too willing believer in miracles. The sup- 

 posed breaks in continuity between stages are, at least in many cases, only disconti- 

 nuities in observation. 



It is the history of specific characters that turns apparent discontinuities into 

 continuities; the lack of it that multiplies mutations into premutations, and premu- 

 tations into hypothetic pangens. Complete histories are indeed rarely attainable, 

 but so much the more significant are they, if just so far as they can be established, 

 they remove all necessity for resort to mutation hypotheses. 



In further illustration, I will refer to the case of the little diamond-dove (Geopelia 

 cuneata) of Australia. In passing from the juvenal color-pattern to that of the 

 adult, we seem to pass to a pattern that is wholly new, and without transitional 

 phases. It looks like an unmediated jump, such as we should expect in biogenetic 

 recapitulation, if mutation were the law of the origin of species. In the adult bird 

 (text-figs. 34 and 36) we have a gray ground with the coverts of the wing very regu- 

 larly marked each with two white dots, one on each side of the feather, equidistant 

 from the apex. In the young bird we have no white dots, but some irregular cross- 



EXPLANATION OF PLATE 88. 



A. Juvenal Geopelia cuneata (Gcl-A2), age 15 days. Hatched June 15, 1899. x 2. Hayashi del., 



June 30, 1899. 



This bird (A 2) differs from its mate (A 1) in having the brownish-yellow edge repeated as a more or less perfect 

 cross-bar in front of the black or blackish bar. The conditions on two rows of coverts show that the anterior yellowish 

 bar is the one out of which the spots arise. The spot (of some brownish yellow with edge) is connected frequently 

 with the "edge," but seems to be either a part of the yellowish edge which is continued forward on the lower edge of 

 many feathers or a part of the anterior yellow bar. It seems to arise about where the edge yellow joins the anterior 

 bar. This pattern marks the tertials, coverts, and scapulars. 



The blackish bar runs into a black streak seen in lower edge of 3 or 4 upper tertials, and in both the upper 

 and lower edges of some of the three rows of coverts. The streak is the equivalent of the ancestral element of the bar. 



The black bar is the same as seen in G. humeralis and in the crested pigeon. Both streak and bar disappear in 

 the adult. 



Three rows of coverts with three yellowish- brown bars are here typical as in other species of Geopelia; and a fourth 

 is quite regular, but it consists of short feathers and is part of the feathers at anterior end of wing. Three rows cover 

 the greater surface of wing. 



B. Juvenal G. cuneata (Gcl-Cl), age 19 days. Hatched July 3, 1899. x 2. Hayashi del., July 22, 



1899. 



Notice that this is not the same individual as the one shown above. It is a slightly older stage in which about 



two rows of the oblique streak, which comes in just in front of the fourth row of coverts, are seen. These have already 



covered the fourth row, one feather of which is seen above next to scapulars and one more at the lower edge of the 



wing. The feathers of this streak have come in within about four days and they differ from other feathers as follows : 



(1) They are more gray, less of brownish tinge. 



(2) The edge is about half the width of that of the earlier feathers. 



(3) The edge runs forward into imperfect cross-bars in which we see very irregular and imperfect spots. These 

 spots were whitish yellow in Gcl-A2, but here they are brownish yellow, just like the color of the terminal edge. 

 These feathers came in much later in Gcl-Al than in (nest-mate) A 2. 



The yellowish edge in this individual is only faintly repeated as a cross-bar in some of the posterior scapulars. 

 Elsewhere it is not repeated, except in faint indications in upper tertials. 



C. Juvenal G. cuneata (Gcl-Cl), same individual as figure B, age 32 days, x 2. Hayashi del., 



Aug. 4, 1899. 



The oblique streak is a little longer, but has apparently no more feathers. A new row of feathers at the lower 

 side of the scapulars has come in. They are grayer than other feathers and have very narrow edges, and these edges 

 are not so light in color as those of first feathers, but are light yellowish-gray. 



In Gcl-A2 these feathers came in somewhat earlier and had brownish-yellow edges two-thirds as wide as the 

 other scapulars. In the first and second rows of coverts notice also three feathers that have come in later; these have 

 narrow, light edges and irregular spots of yellowish-white. 



