part 1] THE ETOLl TIO.X or THE MPAROCERATin.K. 297 



Mammalia ; but, when it is wide, evolution may cease to be guided 

 by environment, and orthogenesis may have free play. If change 

 of environment narrows the margin, a possible result may be sudden 

 extinction. The mode of life which appeared to afford the widest 

 margin of elasticity was the microphagous ; and he put forward 

 as a speculation that the ammonites were not carnivores like 

 modern cephalopods, but had reverted to the microphagous habit. 



Prof. H. H. Swinnertox said that he had been in close touch 

 with the Author while the work was being done, and could 

 testify to the care with which the material had been collected. 

 The Author had exercised due restraint in making new species ; 

 and, in the formation of new genera, had attempted to give them 

 names descriptive of the ammonite, and therefore capable of being 

 incorporated ultimately into a scientilic nomenclature. He had 

 been interested in the account of the way in which the Capricorn 

 stage was eliminated from development, and suggested that one 

 factor in the process may have been the close similarity in general 

 form between the globose early stage and the splnerocone late 

 stage. He congratulated the Author upon the clearness with which 

 he had set forth the subject-matter of his paper. 



Dr. W. D. Lang suggested that the potentiality (demonstrated 

 in this paper in the case of Liparoceratid Ammonites, and 

 by other writers in various groups of animals), in primitive or 

 radical forms for producing similar, definite, and progressively more 

 complex structures in all its descendant lineages, should be distin- 

 guished from the Mendelian Factor, which, at first sight, it would 

 appear to resemble. For example, it might be said that an evolute 

 Liparoceratid carried the factor for involution ; that, by the 

 liberation of an inhibiting factor, the involution became actual. 

 But, on the theory of the Mendelians, each such factor has a 

 corresponding structural basis, so that the more (inhibited) factors 

 are present, the more complex the structure of the nucleus that 

 carries them. With potentiality, on the other hand, the simpler 

 the organism is, the greater are its potentialities ; and, though (as 

 exemplified in Corals and Polyzoa, for example), the method of 

 evolution often suggests that inhibitions are removed (perhaps by 

 environmental changes affecting metabolism generally, and internal 

 secretions in particular), whereby latent potentialities are liberated 

 freehy, as seen in wholesale outbursts or waves of evolution ; yet, 

 there is no reason to suppose that a potentiality is correlated with 

 a definite structure. And, even in the case of the Mendelian 

 Factor, such an assumption is in danger of ultimately leading to 

 absurdity, if, as many Mendelians hold, a new character can only 

 arise by the removal of an inhibiting factor : for the simplest 

 organisms must then have the most complex nuclei — which, if not 

 absurd, is at least improbable. 



The Author, in reply to the President, pointed out that, while 

 it was undesirable to use the names Ammonites striata* and 

 A. capricornus with the wide meaning formerly given to them by 

 stratigraphical workers, yet such terms as ' Capricorn ammonite ' 



