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Show 52 DARWINISM CHAP. song sparrow (Molospiza, mclodia), the fox-c.oloured S]/arrow (Pas erclla iliac:L), the swamp sparrow (Mclosp1za pn1nstl'l s), the black and white creeper (Mniotilta varia), tho w:Ltor-wagtn.il (Seiurus nov::eboracencis), in Turdus fuscoscens and its allic , the difference in the size of the streaks is often very considerabl e. In the sona sparrow they vary to such an extent that in some cases they 0 are reduced to narrow lines ; in others so en la.rgcd as to cover the greater part of the breast and sides of the body, sometimes uniting on the middle of the breast into a nca,rly continuous patch." Mr. Allen then goes on to particularise several species in which such variations occur, giving cases in which two specimens taken at the same place on the same day exhibited the two extremes of coloration. Another set of variations is thus described : "The white markings so common on the wings and tails of birds, as the bars formed by the white tips of the greater wing-coverts, the white patch occasionally present at the base of the primary quills, or the white band crossing them, and the white patch ncar the end of the outer tail feathers arc also extremely liable to variation in respect to their extent and the number of feathers to which, in the same species, these markings extend." It is to be especially notc<l that all these varieties are distinct from those which depend on season, on age, or on sex, and that they are such as have in many other species been considered to be of specific value. These variations of colour could not be presented to the eye without a series of carefully engraved plates, but in order to bring Mr. Allen's measu?"ements, illustrating V<triations of size and proportion, more clearly before the reader, I have prepared <t series of diagrams illustrating the more important facts and their bearings on the Darwinian theory. The first of these is intended, mainly, to show the actual amount of the variation, as it gives the true length of the wing and tail in the extreme cases among thirty specimens of each of three species. The shaded portion shows the minimum length, the unshaded portion the additional length in the maximum. The point to be specially noted here is, that in each of these common species there is about the same amount of variation, and that it is so great as to be obvious at a glance. III Cl) !:::$ ~ <:.> ·;;:: ....... ·-§C-l) -...t..:.. 0 Q) c::, ~ ~ i ~ :iii ~ ~ ~ . d '· ~ ~ ;§ DIAGRAM OF VARIATION Cl) ~ Cl) s;::: ~ !:::$ -£:: 'E:; c;j ~ ~....... ·-::::> Q. e Cl) ·- :S ~ ~ s::: c:u ~ ~ (:$ C,) ~ ..... ~ ,'~, · ~ ~ "' ~ ~· ~ ~ ~ '· 0\ 0\ r~ . ~ ;§ t:: ~ ~ ~ 53 ...; Cl) ..<..l.l >... 0 ..t::. Cl) <ll 't] ..t::. · ~ ..... ..... .0 >... ..s::: t:l C) Q.. 1:::! 'o <ll <ll ~ 'o 1:::! Cl) ..s::: t:: Cl) <ll <ll E -t:: 'C) '!-.> <ll -~ Q.. :s Cl) 0 >... C>:l 0 0\ .~ I:: t:: '§ :;0. ..... Cl) 1:::! <ll ·;:: 0\ 1:::! t:: ;::, ~ ~ ~ ...... t:: :S ::s 0\ 0 t:: E ~ 1:::! <ll 0\ :S · ~ Cl) 3 3 0 0 ~ -t:: Cl) i~ E ..... 1:::! E .0 0\ -t:: tj C) C5 ~ |