﻿Vol. 6 1.] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxili 



mately be given a binominal designation on the Linnaean plan ; but, to mark 

 the fact that it was a mutation, this was connected by the symbol sj~~ 

 with the name of the species from which it was believed to be descended. 

 Thus the name of a descendant of Ammonites subradiatus might be written 

 either as Ammonites subcostarius, Opp. ( V subradiatus, Sow.) or Ammonites 



. — i TT— — ' • In every case the name of the oldest-known form in 



V subradiatus, Sow. 



the developmental series was to be taken as the radicle, although with the 



progress of knowledge this might involve a change in the complete designation 



of any one mutation. 



'From Waagen's statement as to the constancy of mutations, it might be 

 inferred that he believed them to represent discontinuous variations or 

 saltations. This, however, is nowhere definitely expressed by him, and, 

 since he favoured the view that they resulted from some law of development 

 innate in the organism (1869, p. 239, & 1875, p. 243), it might equally well be 

 supposed that he regarded them as stages of a progressive, continuous growth, 

 appearing to us as separate steps only because of gaps in our knowledge. 

 To-day the historian of Ammonites will probably maintain the latter view, 

 and in this he will bf supported by many students of other fossil organisms, 

 even of Vertebrata (see, for instance, Prof. H. F. Osborn, in "The Present 

 Problems of Palaeontology " Pop. Sci. Monthly, Jan. 1905, on p. 230). The 

 question is one of fact, and the term mutation should be maintained, quite 

 apart from the answer that may ultimately be agreed upon. Therefore, 

 palaeontologists should protest against any attempt to restrict the term to 

 professedly-discontinuous variations, especially as these are already provided 

 with the excellent term saltation. This, unfortunately, is the attempt that 

 has been made by Prof. Hugo De Vries, in his book " Die Mutationstheorie " 

 (Leipzig, 1901 : see especially pp. 46-51), a work of such importance and 

 renown that the protest against this particular mutation of terminology must 

 needs be a strong one. 



'A mutation, in the pakeontological and original sense, may be defined as 

 a contemporaneous assemblage of individuals united by specific identity of 

 structure inter se, and by common descent from a known pre-existing species, 

 from which they differ in some minute but constant character or characters. 

 Such mutations are successive steps of a genetic series, and each may be con- 

 sidered as of specific rank and may have its own contemporaneous varieties. 



'The term cir cuius, as Prof. J. F. Blake has kindly pointed out to me, 

 was used by C. G. Ehrenberg, in " Syrnbolae Physicae : Animalia Evertebrata, 

 Series Prima" 1831, to denote a classificatory division less than a Class and 

 greater than an Order. Thus the Anthozoa and Bryozoa each constitute a 

 circulus of the Class Phytozoa. 



'In 1896 the term was employed by Prof. J. W. Gregory, in the British - 

 Museum Catalogue of Jurassic Bryozoa, to denote " certain convenient groups 

 [of species], which are not altogether artificial, but which are not genera in the 

 sense in which that term can be used among Echinoidea and Mammals." Study 

 of the whole chapter shows that the term combined two conceptions, and this 

 has led to a misunderstanding of it in certain quarters. "The essential idea," 

 writes Prof. Gregory {in Hit, Nov. 18th, 1904), " was that the members of such 

 a circulus were not homogenetic, but a casual assemblage of individuals derived 

 VOL. LXI. f 



