94 MKK1STK \\KI.\TION. [PART I. 



this number is \.~>: in N---./,,/,. ,,/// it is 21; in Scotopendrops, 23; in 



' ''///'>"/'< - '. 'Ve. 



In Ceophiiidie, however, tin- total number of inoveable segments is 

 much l.-u-^'.-r, r:ur_'in'_' friin about .'55 to more than 200. Though not 

 ehara.-t.-n-ti.- ..f -.-n.-iM, the iminlttT seems within limits to mark each 

 particular It \\a- foil ml that male GeophiH have fewer segments 



than tin- female. The males of Arthronomoltts longicornis have 51 or 

 ."_' le>_' l.e:ii-inL r segments. while feina'e.s usually have 53 or ~>\. Full- 

 irrosvn female- "t G "I'liiln* terregtria have 83 or 84 pairs of legs ami 

 ami the males nf the -amc species have 81 or 82. In a 

 lar:_'e NeajM.litan specie . '' >///"'///> lii-i'iyatus BauHL. ] the variation 



rather im-ater. In eiu'ht males the number varied between 96 

 and '.''.i; in eleven females, between 103 and 1<>7. <>f two female 



.,/,//,/> rulcatut one inrli\ iilual had 13G and the other 140. NEWPOKT, 

 <../'- Linn. >.. xix. 1>I."-. p. 427, ifcc. 



! ln some of the ( 'hiloj.oda' an increase in the number of segments 

 afiei- i he lar\a hatches, hut the variations mentioned above 

 are n-.-, u-.|eil ae o,-,-iiirinL r in fully formed specimens independently of 

 s due to aije.] 



Iii tin- ton-^/n,^ cases, a tact which is often met in the Study 

 t Variation i- \\<M seen. It often happens that in particular 

 LT--MITU or in particular -pecics. a considerable i - aiige of Meristic 

 N'ariation i- found, while in do-ely allied forms there is little or 

 none. Mxaiiijiles of t hi- are seen in the variability of the (.Jenphi- 

 lida- a- eoin|>areil with the other Chilopoda, and in the neo-tropical 

 spedee of Peripcdus which vary in the number of legs, while P. 

 1ml t'nuri , for in-taiice. i> very constant. It will be noticed that in 

 both th'- c.i t he absolute numbers of parts repeated are con- 

 -iderably higher in the variable than in the i-onstaiit forms. But 

 though "ii'-h cases ha\e gi\-en rise to general statements that series 

 -.f organs containing a small number of members are, as such, less 

 variable than series containing more members, these statements 

 require coii-iih-rable modification: for it is not difficult to give 

 in-tanc,-- both in plant- and in animals, where series made up of 

 a -mall number of members, shew great nieristic variability. 



The bi ai'inj- of t he-e ca-e- on the nature of M ei'ist if Repetition 

 .md th- conception of 1 lom, ,l,,^y will be cou-iJei-ed hereafter. 

 II- re, ho\\e\er, it may be well to call attention to the fact that we 

 have now before ii- cases in which various but characteristic num- 

 b, i - ,,f legs or segments differentiate allied species or genera : that 

 in a liming the truth of the |)octrine of Descent, we have ex- 



pressed our belief thai in each case the spi-cjes with diverse mim- 



b,-i- are descended from some common ancestor. In the evolution 

 of these form-, therefore, the number ha- varied : this on the one 



hand. On the other hand, in (n'njiliiltiti and in Peripabus, WQ see 



riling to N|-\\i'..i;r (Tr-in.i. Linn. SOC, \l\. 1M">, \>. L'C.S), // Alyriapoda 

 |iiur ;i j)iTin.lirnl iiddit i. >n nf . -nii'iits and II-^H, but acconiin^ to later observers 

 thi-i is not true nf all tht Chiln]nl:i. 



