chap, xx.] EXTRA LEGS : POSITION DA A. 4.93 



femur at right angles to the body it may either be placed so that the 

 ventral surface is downwards, or by rotation of the coxa through 90 J 

 the broad posterior surface may be downwards. The rotations of the 

 middle and hind legs are complementary to this. 



In the abnormal specimen the extra pair of legs arise from 

 the anterior side of the normal coxa, forming with it a solid mass 

 and preventing its free rotation in its socket, so that the normal 

 leg can scarcely be moved from the first position with the 

 ventral surface downwards. The common coxal piece is about 

 half as large again as the normal. Posteriorly it bears the tro- 

 chanter of the normal leg, which is of full size and of proper pro- 

 portions. The process of the coxa locking in the ball of the 

 trochanter is posterior, as in the normal front leg. 



Anteriorly the legs SL and SR articulate with the coxa by 

 separate trochanters. Each is separately closed in by a process 

 of the coxa, sip and srp, respectively. Of these processes that 

 of the leg SR is posterior, but that of SL is anterior. Hence 

 the two legs are complementary to each other, and SR is a right 

 leg while SL is a left. This complementary relation is main- 

 tained in all the other parts of these legs. In size the two extra 

 legs are rather more slender than the normal leg. 



It was explained in the introduction to the subject of super- 

 numerary legs that the relations of form between them depend 

 upon the surface of the normal leg from which they arise. Here 

 the point of origin is chiefly anterior to the normal leg, but is 

 also slightly nearer to the extensor or dorsal surface of the coxa. 

 This is not at first sight evident owing to the rotation of the 

 normal leg due to the great outgrowth from its anterior surface ; 

 but nevertheless if the plane of the ventral surface of the normal 

 femur were produced, it would pass ventrally to the ventral 

 surface of the remoter extra leg SR, and therefore this leg is 

 morphologically dorsal to the leg R. The positions of the extra 

 legs are approximately those of the Scheme for the radius marked 

 DAA, and while the surfaces of SR are parallel to those of R 

 when both are extended, the surfaces of SL are inclined slightly 

 to them as in position DAA. In the enlarged Figure III the 

 coxa is rolled forwards so as to exhibit the relation of images 

 between R and SL, and the figure II shews the coxa rolled 

 back to shew the similar relation between SR and SL. 



For the loan of this beautiful specimen I am great!}* obliged to 

 M. Henri Gadeau de Kerville. 



754. Harpalus rubripes (Carabidte) : left posterior tibia bears a supernumerary pair 

 of tarsi. The apex of the tibia is widened and presents two articulations, of which 

 the posterior bears a normal tarsus. The anterior articulation bears a pair of complete 

 tarsi having proximal joints compounded. The two extra tarsi are a complementary 

 pair, the posterior being fashioned as a right. The surfaces adjacent in these two 

 tarsi are structurally posterior surfaces, but they are a little supinated, so that the 

 ventral surfaces are also partly turned towards each other. The position of origin 

 and the relations of the surfaces to each other are almost exactly those which are 



