1002 UROIONI—VARIATION 
UROIONI (properly Uraoni), Owen’s name in 1868 (Anat. 
Vertebr. iii. p. 849) for the group consisting of Archxopteryz, 
UROSTYLE, see PYGOSTYLE, p. 753. 
UTICK, a local name for the WHINCHAT, from its call-note. 
Vv 
VALK, Dutch for FALcon or HAwK, and so used in the Cape 
Colony—Slaauwe Valk (Blue Hawk), being especially the name of 
Melieraz musicus, the so-called “Chanting Falcon,” which has a 
mellow, piping whistle (Layard, B. S. Afr. p. 31). 
VARIATION is a seductive subject that must here be treated 
briefly and with the view of bringing forward a few only of its known 
facts, the consideration of its supposed causes, which are often glibly 
and positively assigned by some writers to account for its origin, 
being wholly out of place, while questions involving the definition 
of “species,” though immediately arising, cannot be entertained— 
since experience shews that they can be rarely answered to the satis- 
faction of any but the respondent. Presuming that readers of 
this article are acquainted with what has been published on the 
subject by Darwin and Mr. Wallace, there will be no need to 
enter at length on the observed facts of Variation as set down by 
those able naturalists. The former of them many years ago de- 
clared (Origin of Species, chap. v.), “Our ignorance of the laws of 
Variation is profound,” and in 1894 Mr. Bateson (Materials for the 
Study of Variation, p. 13) had still to regret that “ Darwin’s first col- 
lection of the facts of Variation has scarcely been increased.”1 Yet 
1 It may perhaps be convenient here to adduce in the most concise way, yet 
almost in Darwin’s own words, what these facts—‘‘ Laws” they have sometimes 
been called—are as enunciated by him :— 
I. (1) Wide-ranging, much diffused and common Species vary most. 
(2) Species of the larger Genera in each country vary more frequently than 
the Species of the smaller Genera. 
(3) Many of the Species of the larger Genera resemble Varieties in being very 
closely, but unequally, related to each other, and in having restricted 
ranges (Origin of Species, chap. ii.). 
II. (4) Multiple, Rudimentary and Lowly-organized Structures are the most 
variable. 
(5) A Part developed in any Species, in an extraordinary way, compared with 
the same Part in allied Species, tends to be highly variable. 
(6) Specific characters are more variable than Generic characters. 
(7) Secondary sexual characters are very variable. 
(8) Distinct Species present analogous Variations ; and a Variety of one 
