THE NATURE OF SPECIES 



closing a discussion at the Entomological Society on "What is 

 a Species?" he remarked ^ that he had never conceived of the 

 origin of a species from one ancestral pair, but always from 

 the change of masses rather than of individuals. He added 

 that it was "the splitting of the single community into 

 separate subcommunities which was the foundation of the 

 process." 



These subcommunities were the kinds of groups for which, 

 in 1896, I suggested the term cir cuius. In a catalogue of the 

 Jurassic Bryozoa, or '*moss-animals," in the British Museum 

 I pointed out that the term species is inappropriate to these 

 groups, because they are not separated by definite boundaries 

 and were not developed by continued divergence into isolated 

 assemblages. The term cnculus was suggested from the 

 analogy between these groups and the knots of people who 

 collected around the speakers in the Roman Forum. Each 

 knot would be crowded near the centre and looser on the 

 margin, whence people would frequently pass to an adjacent 

 circulus. 



The term circulus was also used in 1900 in a work ^ 

 describing a large collection of fossil corals from the Jurassic 

 deposits of Cutch, in western India. Most of the corals 

 came from one reef, which was especially rich in the simple 

 coral Montlivaltia, of which there were more than 2,000 

 specimens. Each circulus of these Indian Montlivaltia shows 

 variations as great as those representing species among the 

 corresponding European corals. One of the flat corals, 

 named M. frustriformis because it is shaped like the frustrum 

 of a cone, has fifteen European analogues; a taller horn- 

 shaped form, M. cornutijormis, corresponds to twenty Euro- 

 pean species, and M. kachensis to eleven. In the European 



* Trans. Ent. Soc. London, 1911, p. XVI. 



^ Palaeontologia Indica, Ser. IX, vol, 2. ^- ' 



r- -I i^ 



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