SUPERNUMERARY APPENDAGES IN INSECTS. 

 EXPLANATION OF PLATE I. 



Fig. 1. — Mygale avicula/ria, natural size. 



,, 2. — Lycosa itquUina, the Wolf Spider. 



,, 3. — Thomasis ahhreviatus, slightly magnified. 



,, 4. — Thomasis lamio. 



,, 5. — Epeira diadema, Common Garden Spider. 



,, 6. — Tegenaria guyonii^ somewhat enlarged. 



,, 7. — Dolomedes Jimhriatus, slightly magnified. 



Qn tbe IFlature of Supernumerary Bppen^aoe0 



in insects* 



THE following evidence relates to about 220 recorded cases of 

 extra legs, antennae, palpi or wings, and speaking of cases 

 in which the nature of the extra parts could be correctly 

 determined, it is found that the following principles are followed 

 (amongst others) : — 



I. — Extra appendages arising from a normal appendage usually 

 contain all parts found in the normal appendage peripherally to the 

 point from which they arise, and never contain parts central to 

 this point. 



II. A. — Extra appendages of double structure are the common- 

 est. I. — Whether separate or in part compound, they consist of 

 a pair of coinplei7ie7itary parts^ ojie being right and the other left. 

 2. — Of the two extra appendages, that which is adjacent to the 

 limb from which they arise, is a limb of the other side of the body. 

 3. — If the pair of extra appendages arise from the a?iterior surface- 

 of the normal appendage, the surfaces which they present to each 

 other are structurally posterior ; if they arise posteriorly^ the adja- 

 cent surfaces are anterior ; if they arise vefitrally, the adjacent 

 surfaces are dorsal, etc. 



II. B. — A single extra appendage is rarely perfect, i. — If it 

 arises from the body, it is formed as an appendage of the side on 

 which it is placed.- 2. — If it arises by peripheral division of an 

 appendage, the parts central to the point of division are commonly 

 right or left as the case may be, while the peripheral part may be 

 a symmetrical and complementary pair. 



These phenomena are important as an indication of the phy- 

 sical nature of bodily symmetry, and in their bearing upon current 

 views of i-he character of germinal processes. — W. Bateson. 



