486 MERISTIC VARIATION. [part i. 



of tarsi. The widened apex bears three supernumerary spurs of 

 which the middle one is thicker than a normal posterior spur. 

 This is no doubt a double spur representing the two posterior 

 spurs of the extra tibiae. The other two extra spurs are ordinary 

 anterior spurs. The relative positions of these spurs are exactly 

 those marked VAA in the Scheme. Of the extra tarsi 3 joints 

 only remain and the two tarsal series are so closely compounded 

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

 first joints the inclination of the ventral surfaces to each other 

 is at an acute angle, thus departing from the Scheme, but in 

 the second and third joints, where they are more separate from 

 each other, the inclination is at approximately the same angle 

 as that of the lines joining their respective spurs. Specimen 

 in General Collection of the British Museum. 



744. Carabus graecus £ : trochanter of right middle leg bears a super- 

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

 joint common. 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. 

 The femur of the extra pair is a single piece but is morphologically 

 double, presenting two structurally anterior surfaces and two structurally 

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

 about 120°. From the apex of this femur there arises a double tibia, 

 also composed of two anterior and two ventral surfaces. This fact is 

 especially clear in the case of the tibia and is proved by the arrange- 

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

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

 the anterior. Now in this tibia there are three spurs, two shorter ones 

 at either margin of the apex, and one longer one with a bifid point 

 between them, which is clearly therefore a pair of 'posterior spurs not 

 completely separated from each other. This A'iew 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 is about the same as in the femur, but is perhaps rather 

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

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

 plete 4-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 

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

 to it. This gives to the base of the double femur a trend dorsalwards: 

 but from the base the femur curves ventralwards so that the nett 

 result is that its apex is actually ventral 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. Now the relative position 

 of the paii- 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 ; 





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