48 fOLuru- PATTERNS. [INTROD. 



win^s of G. rftawni when boiled yield a soluble yellow, which 

 1 1. .I-KIXS (Proc. Cliem. Soc., reported Nature, Dec. 31, 

 I vi | . 'is ;i .l.-rivativo of mycomelic acid, allied to uric acid. This 

 substance turns orange with reagents. The wings of G. rhwtmi 

 turn orange-red when exposed to wet potassium cyanide (Proc. 

 i: - |s71. ],. \\iii) as may be easily seen. 



\Vh.-n these facts, meagre though they are, are considered 

 ,ith the evidence of variability, the suggestion is very 

 that the discontinuity between these several eharac- 

 > of a chemical nature, and that the transitions 

 i one -hade of yellow to another, or from yellow to orange or 

 i phenomenon comparable with the changes of litmus and 

 able blues from blue to red or of turmeric from 

 v,-i: bi..\\n. If such a view of these phenomena were to be 



I. it would. I think, be simpler to regard the constancy of 

 th,. binta t the several species and the rarity of the intermediate 

 \:u . direct manifestation of the chemical stability or 



iliilitv of the i-.. louring matters, rather than as the con- 

 of environmental Selection for some special fitness a^ 

 t.i \\li.is,- nature we can make no guess. For we do know the 

 phenomenon <.f chemical discontinuity, whatever maybe its ulti- 

 mate causes, but ..f tin - hypothetical fitnesses we know nothing, 

 n..t . \.-n whether they exist or no. 



II. C/'<r-i>'ift<'/-/i*. Thus far I have spoken only of dis- 

 continuous v:iri:iti'>ns in colours themselves, but there are no less 

 remarkable instance, , ,f i U.-M-. mt iuu in^ variations in the distri- 

 bution <if i-.ili.ur- in partiri.louivil t'oi-ms. By a combination of 

 tli.-.- in. .!,-. variation- >f ^r> at magnitude may occur. 



()M.- ..f th.- most obvi,.u- cases of this phenomenon is that of 

 the ('at. In Km-.. ] an towns cats an- of many colours, but they 

 ii.-\.-rtl 1( -l.-- fall very n-adily into c.-rtain classes. The chief of 

 tli. - are Mack, tabby, silver-grey and silver brindled, sandy, tor- 

 toi-,, -h.-ll. black and white, and white. ( )f course no two cats 

 hav.- id.-iitical ciilnirini,', but the individual variations group very 



;lv round these Centres, and intermediate forms which cannot at 



on.-.- }>, i-i-t'.-rrei| to any of these groups are immediately recognized 



-"mi-tiling out of the common and ^tran^e. Vet it is almost 

 certain that cats ..fall shades l.re.-d freely together, and there is 

 no r.-a^..ii to viij,|,,,-e that the discontinuity lietwecn the colour- 



u|>- i> in any way (let.-i-miiied by Natural Selection. 

 Aiiot! mple ma\ be aeen in the hog-whelk (I'm-punt 



ln/n/liiM). Tin- animal OCCUTS on nearK the whole British coast. 



rocks or even clay hanl enough to form 



definite , Like nioxt littoral animals, the hog-whelks of 



h locality dilV-T more or |e<s from those of other localities, and 



these ditf- i- IP-. - ma\ be ditten-iu'es ,,t' sixe, te\tuiv of shell, 



of calcification, amount nt ' frilling." vVc. The peculiarities 



