CHAP. XX.] 



EXTRA LEGS : CALATHUS. 



505 



Calathus graecus £ (Carabidre): left anterior tibia bearing a 

 pair of supernumerary tarsi compounded together. The diagram, 

 Fig. 169, I, shews, in projection, the relations of the parts round the 

 tibial apex. As has been explained, the posterior spurs P 1 , P 2 and P 3 

 are really much central to the apex, but they are here represented as if 

 they were projected upon the apex. The head of the tibia is produced 

 posteriorly into a long and narrow process which is formed of the united 

 parts of the two extra limbs and bears the articulation common to the 

 two extra tarsi. The two tarsi stand with their ventral surfaces almost 

 at right angles to each other, but the united dorsal surfaces are almost 

 in a continuous plane. The fifth joints alone are separate, that of RT 

 being small (Fig. 168). 



Fig. 168. Calathus grcecw, No. 776. Left anterior tibia bearing a double extra 

 tarsus. LT, normal tarsus. RT, L'T, extra pair of tarsi. LAS, LPS, normal 

 anterior and posterior spurs. L'A'S', L'P'S', anterior and posterior spurs belonging 

 to L'T. RAS, RPS, anterior and posterior spurs belonging to RT. x, x, dotted 

 line indicating plane of morphological division between extra tarsi, xx, xx, plane 

 of division between the normal and RT. (Specimen the property of Dr Kraatz.) 



In studying this case one source of confusion should be specially 

 referred to. It is seen that though the origin of the extra tarsi is 

 posterior to the normal tarsus, the extra tarsi are as a fact united along 

 their morphologically posterior borders. Nevertheless the position of the 

 spurs shews that it is the anterior surfaces which are morphologically 

 adjacent to each other, for the spurs are arranged in the series A 2 P', 

 P 2 A 2 , A 3 P 3 , and the union of the posterior borders of the tarsi is a 

 result of the modification in the form of the tibia consequent on the 

 rotation of the posterior spur. 



To produce the arrangement here seen, the planes of reflexion would 

 be M 1 and M 8 respectively, and these are almost at right angles to each 



