66 SEX AND VARIETY. [IXTROD. 



SECTION XII. 

 1' \KALI. HI. Hi:i\Vi:iN lUsm.vnXl.TrV nl-'SEX AND DISCONTINUITY 



ix VARIATION. 



The application of the term Discontinuity to Variation must 

 n.,t In- misunderstood. It is not intended to affirm that in dis- 



inuou- Variation then- ran lf between the variety and the 

 type no intermediate form, or that none has been known to occur. 

 ;md it is not even necessary for the establishment of Discontinuity 

 ih.it the intermediate forms should be rare relatively to the 

 ! it., t form of the variety, though in cases of discontinuous 

 Variation this is generally the case: but it is rather meant that 

 tin- perfect form of the variety m<iy appear at one integral step 

 in Descent, either without the occurrence of intermediate grada- 

 tions, "i .it least without the intercalation of such graduated forms 

 in th,' pedigree. 



In the case of the tarsus of Blntta we have seen an example 

 ..t a i,.tal and complete Variation affecting single members of a 

 series of repeated parts, not collectively, but one or more at a 

 tun'- 1 . Such an instance of a Meristic Variation occurring in 

 a -tat,' which is total as regards members of a series but not 

 total a- regards the whole series finds many parallels among 

 Sub-taut i\>- Variations, as, for example, that of the Crab (Cancer 

 ;//</.-) bearing the right third maxillipede fashioned as a chela, 

 whit.- tli.- left third maxillipede was normal. Variations of this 

 nature in plants are of course well known to all. 



V a previoii- place (Section vn.) allusion was made to the 

 familiar but very curious analogy between members of a series of 

 M eristic parts and separate organisms. The facts of Variation bring 

 oin thi- analog in many -insular ways, and in speaking of the 

 totalitv of Variation it is necessary to hear these facts in nn'nd. 



/ 



N only an- there abundant instances of independent division 

 or multiplication ,.f -ingle m< -miters of Meristic series, but as 

 ha- l>e. -n -aid. -ingle member- of such series may thus inde- 

 pendently an, 1 singly undergo qualitative or Substantive Variation, 

 being treated in tin- ph\-ical sy-tem of the body as though they 

 - -pai-ate units. In Variation, therefore, though it will be 



ption tliut the variation may .-it !ea-t smn, .times be congenital. Supposing 

 howe\er Unit tliis -hull lie found hereafter not to be the ease, I do not think that 

 tin- ill- in, -t. Mil- ilniwn fi-,,m the t'ui't-i \vill he less vuliil. The conclusions as to 



the ileliniteness of the two t\|n^, ;ill>l the Vel :| t ion -h i ] is of the several parts of each 



il purts of the other, would still hold ^ood. Then- are besides in other 

 I'"' -lee- of similar nuinei ieai Variation, as for example, in the number of 



joint- in the antenna, of I'rioiiida', where the hypothesis of change on renewal is 

 imp., -sih],.. from which a -imiliir argument ini^ht be drawn; but on the whole I 

 '"^ i"' as it stands, taking the case of Blntta as an 



-ily a, ,-. ilile and be.-au-e. from die fewness of the joints 

 roin-i-ini d. tli,- i-siirs are singularly char. 



' See Note at tile end of S, etioll XI. 



