550 ON HEREDITY. 



germplasin as luay be called spoiitaiieoas, leadiiij"; to such an altera- 

 tiou iu its character as may produce a new variatiou ; or, 



(2) Whether their origin be accidental, or due to habits, or to the 

 nature of the surroundings, such as climate, food, etc. 



Professor Weismann has pointed out with great Ibrce the necessity 

 of distinguishing between these two kinds of " acquired characters," 

 and he has suggested two terms, the employment of which maj^ keep 

 before us how important it is that these different modes of origin should 

 be recognized. Characters which are produced in the germ-plasm it- 

 self by natural selection, and all other character which result from this 

 latter cause, he names hlastogenic. He further maintains that all blasto- 

 genic characters can be transmitted ; and in this conclusion, doubtless 

 most persons will agree with him. On the other hand, he uses the term 

 somatogenic to express those characters which flrst appear in the body 

 itself, and which follow from the re-action of the soma under direct ex- 

 ternal influences. He includes under this head the effects of mutila- 

 tion, the changes which follow from increased or diminished perform- 

 ance of function, those directly due to nutrition, and any of the other 

 direct external influences which act upon the body. He further main- 

 tains that the somatogenic characters are not capable of transmission 

 from parent to offspring, and he suggests that in future discussions on 

 this subject the term " acquired characters" should be restricted to 

 those which are somatogenic. 



That the transmission of character so required can take ])lace is the 

 foundation of the theory of Lamark, who imagined that the gradual 

 transformation of species was due to a change in the structure of a part 

 of an organism under the influence of new conditions of life, and that 

 such modifications could be transmitted to the offspring. It was also 

 regarded as of importance by Charles Darwin, who stated,* that all the 

 changes of corporeal structure and mental power cannot be exclusively 

 attributed to the natural selection of such variations as are often called 

 spontaneous, but that great value must be given to the inherited effects 

 of use and disuse, some also to the modificatiou in the direct and pro- 

 longed action of changed conditions of life, also to occasional rever- 

 sions of structure. Herbert Spencer belie ves,t that the natural se- 

 lection of favorable varieties is not in itself suflScient to account for 

 the whole of organic evolution. He attaches a greater importance 

 than Darwin did to the share of use and disuse in the transmission 

 of variations. He believes that the inheritance of functionally pro- 

 duced modifications of structure takes place universally, and that 

 as the modification of structure is a vera causa as regards the indi- 

 vidual, it is unreasonable to suppose that it leaves no traces in pros- 

 terity. 



On the other hand, there are very eminent authorities who/ contend 



'Preface to 2cl edition of Descent of Man, 1885 ; also Orifi'm of Species, 1st ed. 

 t '"Factors of Orjjauic Evolutiou," Xineteenth Centnrn, 188(;. 



