I002 UR OIONI— VA RIA TION 



UEOIONI (properly Uroeoni), Owen's name in 1868 {Anat. 

 Vertebr. iii, p. 849) for the group consisting of Archseopteryx. 



UEOSTYLE, see Pygostyle, p. 753. 



UTICK, a local name for the Whinchat, from its call-note. 



VALK, Dutch for Falcon or Hawk, and so used in the Cape 

 Colony — Blaauive Valk (Blue Hawk), being especially the name of 

 Melierax 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. Presviming that readers of 

 this article are acquainted with what has been published on the 

 subject by Darwin and Mr. Wallace, there Avill 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 

 Stiidy of Variation, p. 1 3) had still to regret that " Darwin's first col- 

 lection of the facts of Variation has scarcely been increased." ^ Yet 



^ 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 freq^uently 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 



