244 Scientific Intelligence. 



one of the most important of recent contributions to the subject 

 of evolution. Like most American writers on evolution, the 

 author attributes only a secondary importance to the principle of 

 Natural Selection. In place of it he uses the expression physical 

 selection, and explains it as " the production of suitable modifica- 

 tions by the action of forces which changed in a similar way 

 large numbers of the same species, perhaps nearly all the indi- 

 viduals in the same locality or same habitat, within a compara- 

 tively limited period of time. The changes express the general 

 tendencies to modification due to the response to physical causes 

 on the part of the common radical and common organization. 

 Another principle recognized is that whatever the order in the 

 progressive development of a group, there is ordinarily the 

 reversal of this order in retrogressive or degradational develop- 

 ment. A third is acceleration in development, or the tendency in 

 any variation in a progressive series to be inherited at earlier and 

 earlier stages. A fourth is the fundamental principle of Agassiz, 

 the basis of much of Mr. Hyatt's work, the parallelism between 

 the steps in the development of an individual and those in the 

 history of the group to which it belongs. These and other general 

 ideas, brought out in Mr. Hyatt's essay of 1883, on the Fossil 

 Cephalopods in the Museum of Comparative Zoology, are exem- 

 plified in various ways throughout this new elaborate work, and 

 illustrated by excellent figures of all the species of the group of 

 Ammonites under consideration — in which illustrations Mr. Hyatt 

 shows that he is also an artist. An analysis of the work would 

 require an article of many pages. 



Among the principles one of a physiological character appears 

 hardly to have its importance recognized by Mr. Hyatt, and is 

 often overlooked by others. It is the familiar principle on which 

 the breeder relies, the tendency of a variation, however begun, 

 to become augmented by interbreeding, when the variety is one 

 that admits of it. It is not "like producing like," but producing 

 more than this; it is augmenting or accumulating in its effects, 

 and often until the likeness in one character or another is largely 

 lost ; and it may affect thus either a generic, family, or tribal charac- 

 ter as well as a specific ; and all this by simply continued inter- 

 breeding, with healthful feeding and nothing more. Darwin 

 began his work on the Origin of Species by illustrating the prin- 

 ciple at length, but he failed to give it its true place because he 

 assumed that variations in the individuals of a region would be too 

 few for success without aid from natural selection. But if a varia- 

 tion takes place simultaneously or nearly so in most of the associa- 

 ted individuals of a region, as Mr. Hyatt holds, and as is probable 

 amidst like environment conditions, then it may work as if under 

 man's guidance, without natural selection or further physical 

 selection. And the results under such circumstances will be 

 permanent and normal, free from the extravagances of man's 

 forcing work, because nature's healthful work is always slow and 

 normal. This physiological law of accumulative breeding, while 





