MancJiester Memoirs, Vol. Ix. 



PRESIDENTIAL ADD: 

 Animal Symmetry and the Differentiation of Species. 



By The President, 

 Professor Sydney J. HiCKSON, M.A., D.Sc, F.R.S. 

 January nth, igi6. 



In the early years of the 19th century Baron Cuvier 

 constituted four great divisions for the Animal Kingdom : 

 the Animalia Vertebrata, the Animalia Mollusca, the 

 Animalia Articulata and the Animalia Radiata. In the 

 first three of these divisions the organs of sense and 

 motion are symmetrically arranged on the two sides of an 

 axis. In the last division they are disposed like rays 

 round a centre. 1 



This early attempt to establish a system of classifi- 

 cation of the animal kingdom based on a separation of 

 animals showing a radial symmetry from those showing 

 a bilateral symmetry never met with any real success. 

 Many of the groups of animals that were included in 

 Cuvier's division Radiata proved to be widely separated 

 from one another by anatomical characters, and some of 

 them, such as the Echinodermes and the Entozoa, proved 

 to be more closely related to bilaterally symmetrical 

 animals than they are to the other Radiata. 



But if we recognise, as we must, that body symmetry 

 is not a good guide to a scientific classification of animals, 

 it may be worth while to consider the circumstances that 



1 "Dans tous les precedens, les organes du mouvement et des sens 

 etaient disposes symetriquement aux deux cotes d'un axe. Dans ceux-ci, 

 ils le sont circulairement autour d'un centre." Cuvier. " Le Regne 

 animal," 181 7, p. 61. 



February 12th, igi6. 



