490 MERISTIC VARIATION. [part I. 



Right hind leg (Fig. 159, I), the tibia is dilated towards the 

 apex which presents dorsally two emarginations instead of one 

 as usual. On the ventral aspect of the apex there are two whole 

 spurs PS, A"S" and a double one AS, A'S', between them. 



These spars give the key to the nature of the structure. The 

 proximal tarsal joint gives off a process on its anterior side and 

 is then continued to bear a normal termination as shewn in the 

 figure. The process from the first tarsal bears a second tarsal 

 from which the termination has been broken off. The extra parts 

 are as in the figure, being covered ventrally from edge to edge 

 with papillae, and having no longitudinal cleft in the middle line 

 like the normal tarsus. 



Looking at these tarsal joints alone, the real nature of the 

 extra parts does not appear, for the anterior and posterior surfaces 

 of the normal tarsi are not differentiated from each other, and 

 hence it is not possible to say of what parts the supernumerary 

 limb is made up. Fortunately, however, the tibial spurs are 

 normally distinguishable from each other, for the anterior spur 

 is a short spur while the posterior is a long thin spur. Now the 

 spurs present in this case are firstly one long posterior spur PS, 

 and then three short anterior spurs, of which two are united for 

 part of their length .4$, A'S'. The extra spurs are thus both 

 anterior spurs, that of the extra tarsus which is nearer to the 

 normal being united to the normal anterior spur. Hence this 

 case is a case of a supernumerary pair of appendages compounded 

 together in the Schematic Position A, having the posterior sur- 

 faces adjacent and suppressed. 



Right middle leg. (Fig. 159, II.) In this case there would 

 have been more difficulty in making out the real nature of the 

 parts ; for in the normal middle leg the anterior spur is not so 

 much differentiated from the posterior one as it is in the hind 

 leg : but having this case for comparison it is easy to see that 

 this also is a case of a pair of appendages similarly compounded 

 in Position A. This case differs from that of the hind leg in 

 the fact that the parts are not so fully formed, and especially 

 the anterior spur of the nearer extra tarsus is scarcely separated 

 from the anterior spur of the normal. By turning the specimen 

 over in the light however, its form can be made out to be that 

 shewn in the figure. When the specimen was received by me 

 the parts present were as shewn in the figure, but when originally 

 described by vox Heydex there was a third joint in the extra 

 appendage which was small and elongated, and to all appearance 

 it was the original termination and nothing had been broken off. 

 For the loan of this specimen I am indebted to Dr L. VON Heydex, 

 who originally described and figured it in Dent. ent. Zt., 1881, 

 xxv. p. 110, Jigs. 27 and 28. 



In the two following cases there was nothing to differentiate 



