1891.] which follow total extirpation of the fore-brain. 159 



body, that febrile changes may be induced independently of this 

 mechanism. 



(2) On the nature of Supernumerary Appendages in Insects. 

 By W. Bateson, M.A., St John's College. 



[Abstract.] 



The author exhibited a number of specimens in illustration of 

 this subject. 



The evidence related to about 220 recorded cases of extra 

 legs, antennas, palpi or wings, and particulars were given as to 

 the mode of occurrence of these structures. 



Speaking of cases in which the nature of the extra parts could 

 be correctly determined, it was found that the following principles 

 were generally followed : 



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. Such appendages are commonly double. The axes of the 

 three appendages then stand in one plane, one being nearer to the 

 normal appendage and one remote from it. In structure and 

 position the nearer limb is the image of the normal limb in a 

 mirror perpendicular to the plane in which the limbs stand, while 

 the remoter extra appendage is the image of the nearer one in a 

 remote mirror parallel to the first. Thus if the normal limb is a 

 right limb, the nearer supernumerary is a left and the remoter a 

 right, and vice versa. 



An extra appendage sometimes occurs which is apparently a 

 single structure. In all instances in which the matter could be 

 determined, it was found that the apparently single appendage in 

 reality consisted either of two anterior halves or of two posterior 

 halves of a pair of appendages conforming to the law stated. 

 Probably therefore no extra appendage is morphologically single. 



It was pointed out that these phenomena are important as 

 an indication of the physical nature of bodily symmetry, and 

 in their bearing upon current views of the character of germinal 

 processes. 



The author expressed his indebtedness for information, or the 

 loan of specimens, to Messrs H. Gadeau de Kerville, Pennetier, 

 Giard, Kraatz, L. von Heyden, Dale, Mason, Westwood, Water- 

 house, N. M. Richardson, Janson, Reitter, &c, and especially 

 to Dr Sharp for much help and advice in examining the 

 specimens. 



