48G MKKlsTir VARIATION. [I'AKT I. 



"t tar-i. The widened apex l)cars three supernumerary spurs of 

 which tin- middle i. DC is thicker than a normal posterior -pur. 

 'I'lii- i~ no doubt a double spur representing tin- t \vo posterior 

 -pur- of tin- i-xtra tibia-. The <>\ her two extra spurs are ordinary 

 anterior -pur-. Tin- relative positions of these spurs are exactly 

 those marked \'AA in the Scheme. Of the extra tarsi 3 joints 

 only remain and the two tar.-al series are so closely compounded 

 that superlieialK they seem to form one tarsus only. In their 

 tir.-t joints the inclination of the ventral surfaces to each other 

 i- at an <n-,it,- angle. thus departing from the Scheme, but in 

 the -econd and third joint-, where they are more separate from 

 h nt her, the inclination is at approximate!} the same angle 

 as that of the lines joining their respective spurs. Specimen 

 in (ieneial Collection of the British Museum. 



74 1- Carabus graecus ^ : troehanter of right middle leg bears a super- 

 numerary pair of legs having trochanter, femur, tibia and 1st tarsal 

 j"int ciiiiiiiiuii. The coxa of the normal leg is enlarged and the trochan- 

 ter has two heads, of which the anterior belong to the extra pair of legs. 

 'I'he t'eiuur of the extra pair is a single piece but is morphologically 

 double, presenting two *trn<-tii milt/ anterior surfaces and two structurally 

 ventral surfaces, the latter being inclined to each other at an angle of 

 aliout 1 _'(). From the apex of this t'eiuur there arises a double tibia, 

 also < ...... posed of two anterior and two ventral surfaces. This fact is 



especially dear in the case of the tiliia and is proved by the arrange- 

 ment of the spines and spurs. In a normal tibia there are two spurs, 

 "ne posterior and one anterior, and the posterior spur is longer than 

 the anterior. Now in tin's tibia there are three spurs, two shorter ones 

 at either margin of the apex, and one hniiji-r one with a bifid point 

 between them, which is dearly therefore n pair of posterior spurs not 

 completely separated from each other. This view of the structure of 

 the double tibia is equally evident from the arrangement of the 

 remainder of the spines on its surfaces. In it the inclination of the ven- 

 tral surfaces i- aliout the same as in the femur, but is perhaps rather 

 more acute. The 1 >t tarsal joint is similarly a double structure. Its 

 apex presents two articulations, but while the posterior bears a com- 

 plete ! jointed continuation, the anterior bears only a single aborted 

 joint, from which possibly some portion has been detached, but this is 

 not certain. 



The relations of the parts are a little obscured by the fact that the 

 normal tibia is slightly bent. The double part of the trochanter lies 

 \ery nearly anterior to the single part but it is also somewhat dorsal 

 to it This ^ives tn the base of the double femur a trend dorsalwards: 

 but from the base the femur Curves vent ralwards so that the nett 

 result is that its ape\ is actually \entral to the apex of the single 

 femur when both limbs are extended. This curve of course gives the 

 femur an abnormal form which is increased by the fact that it is 

 perceptibly shorter than the single femur. No\v the relative position 

 of the pair of extra limbs is that marked VAA, and as it stands when 

 extended the apex of the double femur and the peripheral parts of the 

 double limb stand in the Position VAA with regard to the single limb ; 



