chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 507 



lei to each other and to the long axis of the tibia. The tarsi tr and t 3 

 separate in the first joint. 



The relative positions are shewn in the diagram, and it is thus seen 

 that the planes of reflexion M 1 and M' 2 are inclined to each other at an 

 acute angle. 



This specimen was kindly lent to me by Dr L. von Heyden and 

 was first described and figured by Mocquerys, Col. anorm., 1880, p. 

 65, fig. 



It is difficult to observe the two foregoing cases without sus- 

 pecting that the fact that they deviate from the normal symmetry 

 of extra parts may be connected with the normal modification 

 of the anterior tibia in these Carabidw. It should be remembered 

 that the tibia and tarsus of the unmodified leg of a beetle are 

 very nearly bilaterally symmetrical about the longitudinal median 

 plane of the limb, but in this leg of these forms the symmetry 

 is lost. Possibly then the upsetting of the ordinary rules for 

 the Symmetry of extra parts may follow on this modification. 

 The difference between the two cases moreover is possibly due 

 to the fact that in one the extra parts are on the posterior surface 

 of the leg, while in the other they are on the anterior. Since the 

 normal limb is not bilaterally symmetrical it is reasonable to expect 

 that the results would differ in the two cases. One other case 

 of a pair of extra tarsi in the fore leg of a male Calathus is re- 

 corded (No. 777 a), but insufficiently described. It is to be hoped 

 that a few cases of extra tarsi in the fore leg of male Calathus 

 ' or Pterostichus may be found, and it is very possible that such 

 a case even in Carabus would help to clear up these points. 



77 a. Calathus fulvipes <j (Carabidre) : tibia of right fore leg bears pair of extra tarsi. 

 ' [Fig. and description inadequate.] Pekty, Mitth. nat. Ges. Bern, 1866, p. 307, fig. 5. 



(10) Nine other cases departing from the Schematic Positions. 



Each of these needs separate consideration. 



"778. Platycerus caraboides (Lucan.) : left hind tarsus has form 

 shewn in Fig. 170. The terminal joint had only one 

 claw. R and L' are presumably the extra pair, but it 



I will be seen that they arise at separate places from the 

 3rd tarsal joint. Otherwise, they stand approximately 

 in Position Y. Described originally by Mocquerys, 

 Col. anorm., p. 67, fig. 

 779. Philonthus ventralis (Staphylinida?) : third joint 

 of right posterior tarsus bearing supernumerary termi- 

 nation of double structure. The apex of the third joint £ 

 is enlarged, and at a point anterior and slightly dorsal FlG 17 q 

 to the articulation of the normal fourth joint the super- pi a ty C erm ca- 

 raboides, No. 778. Left hind, tarsus from posterior surface. 

 L, the presumably normal apex, has only one median claw. R 

 and L', arise separately from the 3rd joint. (In Rouen Mus.) 



