chap, xx.] EXTRA LEGS: POSITION A. 489 



right tarsus (Fig. 159). This is a very important case as a clear 



Fig. 159. Prionus coriarius, No. 750. I. Apex of tibia of right hind leg with 

 its tarsus. II. Similar parts of right middle leg. (The property of Dr von Heyden.) 



PS, AS, posterior and anterior tibial spurs belonging to the normal leg. A'S', 

 A"S", the spurs of the extra legs, all structurally anterior spurs. A, anterior 

 surface. V, ventral surface. (The property of Dr von Heyden.) 



illustration of the mode in which double supernumerary limbs 

 may be compounded together so as to closely simulate a single 

 limb. Each of the extra parts in this case in the original account 

 was described as a single extra limb, but as will be shewn, each 

 is really composed of parts of a complementary pair. Cases of 

 this kind suggest very strongly that other cases of supposed single 

 extra limbs are really instances of double extra limbs in which the 

 duplicity is disguised. 



