286 THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 



Ontogeny in a sense stands midway between heredity and environment, that 

 is, the somatic expression of purely hereditary forces depends both upon the 

 continuity of environmental conditions and on the continuity in the ontogeny 

 itself. If there is a revival of an ancestral or bygone environment, there may be 

 more or less of a revival of ancestral ontogenic characters. 



Wherever the environment or the ontogeny differs from its typical condition 

 we discover somatic changes, which are variously known as modifications, 

 somations, accommodations, individual adaptations. Some of the " varia- 

 tions' ' of Darwin and "fluctuations" of other authors are undoubtedly expres- 

 sions of ontogeny rather than of heredity. 



Ontogenic processes are so closely related with hereditary predispositions 

 that it has often been difficult to draw the line between the predisposition and 

 that which is added. The following summary includes the processes in which 

 there appear to arise some of the chief ontogenic modifications of typical heredity. 



1. Revival of ancestral (recessive or latent characters) through the revival 



of ancestral environment. 



2. Acceleration in the rate of ontogeny through functional and other causes. 



3. Retardation in the rate of ontogeny through loss of function and other 



causes. 



>> 



4. Progressive individual development or "ontogenic development. 



5. Retrogressive or "ontogenic degeneration.' ' 



6. Somations or modifications of the somatic cells through direct action 



of the physical environment. 



7. Somations or modifications through the law of use and disuse. 



8. Somations through changed social, reproductive, mutative, and traditional 



relations 



i 



9. Somations through changes of function 



1 ... We owe to Dr. Arbuthnot Lane a most interesting series of studies upon the influences of various 



hnrlv TTp nrnws ormnlnsivftlv t,hat, individual adaptation not only produces 



human 



profound modifications in the proportions of the various parts, but gives rise to entirely new structures. 



His anatomy and physiology of a shoemaker* shows that the life-long habits of this laborious trade 

 produce a distinct type, which if examined by any zoological standard would be unhesitatingly pronounced 

 a new species. The psychological analysis which a Dickens or Balzac would draw, showing the influences 

 of the struggle for existence upon the spirit of this little shoemaker, could not be more pathetic tnan 

 Dr. Lane's analysis of his body. The bent form, crossed legs, thumb and forefinger action, and pecuu 

 jerk of the head while drawing the thread, are the main features of sartorial habit. The following are oniy 

 a few of the results : The muscles tended to recede into tendons and the bony surfaces into wnicn t y 

 were inserted tended to grow in the direction of the traction which the muscle exerted upon them, 

 articulation between the sternum and the clavicle was converted into a very complex arthrodi jo 



'! 



almost a ginglymoid articulation 



bodies 



that they had ceased to rise and fall with sternal breathing, and that respiratio 

 diaphragmatic. The region of the head and first two vertebra of the neck ^f^ 

 ;ransverse process of the right side of the atlas, toward which the head was ^'^ 

 with the under-surface of the jugular process of the occipital bone, a smau yn . 



surrounded this acquired articulation, but there was no appearance of a caps 

 : the axis was united by bone to the corresponding portion of the third cervical 



Journal of Anatomy and Physiology, 1888, p. 595. 



