404 NATURAL SCIENCE. June, 



of those from the alleged but contested Hamilton fauna above, the 

 argument from such evidence would be entitled to serious con- 

 sideration." 



Organic Equilibrium. 



In our last number, the review of Mr. Bateson's book on Variation 

 gave occasion for some remarks on continuity and discontinuity in 

 species. It will be remembered that the guiding idea of that book is 

 that a species may change from one specific type to another by a 

 sudden jump, or, as Mr. Bateson phrases it, by a discontinuous varia- 

 tion. In the words of Francis Galton, the species passes from one 

 position of organic stability to another. It may therefore be interesting 

 to remind our readers that similar ideas were long ago put forward by 

 two American biologists, who, however, went even further in supposing 

 a sudden passage of more than one species from one genus to another. 

 E. D. Cope in 1868 discussed the Origin of Genera (Proc. Acad. Nat. 

 Set. Philadelphia), and showed, as he believed, that genera were grades 

 of organisation, entered upon by more than one species at a time, and 

 often entered upon with some suddenness. He explained these 

 metamorphoses of species by a reference to metamorphoses or 

 periods of rapid development in the life of individuals. When 

 such periods corresponded with the period of reproduction, then the 

 offspring would, he considered, be more liable to variation. 

 When the metamorphosis of the individual was subsequent to 

 reproduction, the offspring, and therefore the species, would remain 

 unchanged ; but when the metamorphosis occurred before the period 

 of reproduction, the characters would be transmitted to the offspring, 

 and the species would enter on a new phase. Cope compared these 

 points of change to those critical points of temperature at which 

 sudden changes take place in the molecular constitution of matter, 

 and he applied to them the term " expression-points." Carefully 

 examined, however, Cope's principle of " Acceleration " is seen to be 

 essentially the same as what is now called the " Law of Earlier 

 Inheritance " ; and those who believe that the latter " Law " 

 expresses the process of evolution of species and genera, certainly do 

 not believe in any sudden change. 



W. H. Dall, writing in the American Naturalist for March, 1877, 

 similarly ascribes such supposed sudden changes " to the action of 

 a law of development which finds expression in the paradox that the 

 same species may belong to different genera." That sudden leaps 

 may be due to the gradual accumulation of minute differences, he 

 exemplifies as follows : — " In a sloping gutter of a paved street not 

 too cleanly swept every one will have noticed on a sudden shower how 

 small particles of earth and other materials will sometimes act as a 

 dam, producing a puddle, which, relieved by partial draining, may for 

 a time remain in statu quo. A time comes, however, when the 

 gradually-accumulated pressure suddenly sweeps the dam before it 



