SEGMENTATION 



73 



added. If they spring from the actual base of the appendage 

 then two complete appendages may be developed in addition to 

 the normal one. We must therefore conclude that in any point 

 on a normal appendage the power exists which, if released, may 

 produce a bud containing in it a paired set of the parts peripheral 

 to this point. 



Next the geometrical relations of the halves of the super- 

 numerary pair are determined by the position in which they stand 



D 



nnA 



DA 



DDP 



Fig. ii. Diagrams of the geometrical relations which are generally exhibited 

 by extra pairs of appendages in Arthropoda. The sections are supposed to be 

 those of the apex of a tibia in a beetle. A, anterior, P, posterior, D, dorsal, V, 

 ventral. M 1 , M 2 are the imaginary planes of reflexion. The shaded figure is in 

 each case a limb formed like that of the other side of the body, and the outer 

 unshaded figures are shaped like the normal for the side on which the appendages 

 are. On the several radii are shown the extra pairs in their several possible re- 

 lations to the normal from which they arise. The normal is drawn in thick lines 

 in the center. 



