CHAPTER V. 

 LINEAR SERIES continued. 



VARIATION IN ARTHROPODA. 



Tin: occurrence of Hoimeosis among the appendages of Ar- 

 thropoda is illustrated by a small but compact body of evidence. 

 TO tin- evidence special value may be attached, not because it 

 i- likelv that in the evolution of the Arthropods variations have 

 reallv taken plan-, in magnitude comparable with those now to 

 In- described, but rather because these cases give a forcible illus- 

 tration of possibilities that underlie the common and familiar 

 phenomena of Mrristic Repetition. Of these possibilities they 

 are indeed " Instances Prerogative," salient and memorable ex- 

 amples, eiiuntiating conditions of the problem of Variation in 

 a form that cannot be forgotten. Facts of this kind, so common 

 in flowering plants, but in their higher manifestations so rare 

 in aiiimaU. hold a place in the study of Variation comparable 

 pel ha ] i>. uith that \vlnch the phenomena of the prism held in the 

 studv of the nature of Light 1 . They furnish a test, an elenchus, 

 which any hypi'the-i- profiling to deal with the nature of organic 

 I!. | ii titioM and Meristic Division must needs endure. 



[NSECTA. 



;:,. Cimbex axillaris (a Saw-tly), having the peripheral parts 



of the left antenna developed as a foot. The right antenna is 

 normal, ending in a club-shaped terminal joint. In the left an- 

 tenna the terminal joint is entirely replaced by a well-formed 

 f..ot, ha\ing a pair of normal claws and the jtltintula between 

 them ( Fig. III). This foot is rather smaller than a normal foot, 

 but is perfectly formed. The iv>t of the antenna, so far as the 

 point at which the club should begin is normal in form, but is 

 a little Mnaller and thinner than the same parts in the right 

 antenna. KUAATX. (',.. /V///. ,/. /f/.xv///-., LsTU, XX., p. 377, PL 



1 See tlie well-known passage in Nov. Org., u. xxii. 



