54 IflgOBLLANKoUs KXAMI'LKs. [ISTROD. 



,11. .1. No mark. (1 \ariati.ui in th-- upper-ides was to be seen. 

 perimen- were all from th- Khasia hill-. Assam, but then- 

 no evidence that all were tl\ing to-vthcr. 



< ), ..f tin- in el int." j .-\Hiiijili-v of <li>..-unt inuous Variation iu 



th.- ca ..... f ... In- marking or c\--.spots. Upon 



t),i, - u ! 'liin- u.-'-.l li.-ri- I"- said as the -\ id'-iu-i- will be given in 



(I. -tail in tli- i-.'iir-- "f tlii- \nlmiif (866 ' 'liap. XIII.). 



SECTION X. 



I'M ".VIIXITIT IN SUBSTANTIVE VARIATION. MlSCELtANEOUS 



K.\ \MI'i I - 



'he discontinuous occurrence of Substantive Variation, the 



manif.-tations an- inanv and diverse. We have seen that in such 

 features as si/.', <,!,. nr, and culoni--|iat tej-ns, Variations may be 

 li-.-. nit inn.. ii-. and a form may thus result, differing markedly 

 iVi.m tin- t\|>.- which begot it. Variation in the proportions or 

 tin- ..n-titutiiui .f .-s.-ntial jiart> may no less suddenly occur. 

 'I'll, ran^.- ..!' tln-se jiheiniini-iia is a large one, but. tor the purposes 

 <>f thi- Iiitmdnetion :i few xampl.-s must suffice in general 

 illustration of their scop.-. 



A discontinuous variation which is familiar to all is that of 



rersed" vaiieties, ojiecially of MolhiM-s and Flat-fishes. Such 

 \ ari'-t 1- - an- formed as ..jit ieal ima^i > of the body of tin ' type. In 

 both ..f tin- ^n.nps nann -d, >ome species are normally right-handed. 

 ntln-r- l.ein^ normally left-handed, while as individual variation-- 

 rev. i-. d . samples are found. In .Molluscs this is not peculiar to 

 1 .pods uith spiral shells, but may occur also both in Lima- 



cid.-e islii;^-) 1 and in Laim llibraiichs a . Such variation is commonly 

 discontinuous, and th- two conditions are alternative. The fact 

 that the reversed condition may become a character of an estab- 

 li-hfd pace is- familiar in th.- case of /'//*//* untufinis. This shell 

 is toiind in abnndanc.- as a fossil of the Norwich Crag, such 



iin.il-> K. in- normally 1.1't-handed. though the same species at 

 th.- pr..-eiit da\ i- a ri-ht- handed one. Of the left-handed form a 

 CO|MI,\ was discovered \>\ MAI-ANI>I;I:\V on the rocks in Vigo Bay :: . 



was there a.oeiated with certain other shells proper to the 

 N"i \\ich ( Iraff. This discovery BI .-mL-d to Edward Forbes to be so 

 remarkable that he looked ,,n it as corroborative evidence of a 



| ; d connexion between the fauna of Vig.> Bay and the Crag 

 fosailfi . Jeffreys had the same variety from Sicily 4 . 



1 F..1 .-MIIMJ,]... ;i Mii.stml Ariii. I'.vriM'N. -A.;/;-. (/,- Coin-]/., xxxil. 1884, p. r!"(i 

 and inuny i.ti 



Mm mil Tellina, PIBOHBB, I'., ./.,;/;. </, Conch., xxvin. 1880, p. 234. The 



i.li-.l in >. M'lal uihrr 



. I/.". .V. //.. isl'.i, ,,. .307 



4 r.nt. c,,n,-ii., i. ].. :(_'.;. 



