934 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



a small piece of the leaf of a begonia, planted in moist earth, a new plant 

 with all its parts may arise. It is evident that the existing parts of an organ- 

 ism, if not too specialized, possess the power of restoring parts that are lost ; 

 under ordinary circumstances this power is latent. The growth of tumors is 

 perhaps allied in nature to regeneration. A study of regeneration shows that 

 in many cases the process of building anew follows the same course as the 

 original embryonic growth. It is properly a phenomenon of heredity. 



The Inheritance of Acquired Characters. No topic in heredity has been 

 more debated during the past fifteen years than that of the possibility of the 

 transmission to the offspring of characteristics that are acquired by the parents 

 previous to the discharge of the germ-cells, or, in the case of the mammalian 

 female, previous to parturition. Obviously, no one denies this possibility in 

 the unicellular organisms, where reproduction by fission prevails, for there the 

 protoplasm of the body of one parent becomes the substance of two offspring ; 

 in the transformation nothing is lost, and hence whatever peculiarities the ances- 

 tral protoplasm has acquired are transferred bodily to the descendants. But 

 in multicellular forms, where sexual reproduction exists, the case is very dif- 

 ferent, for here whatever is transmitted is transmitted through germinal cells, 

 or germ-plasm, as the hereditary substance contained in the germ-cells is now 

 commonly called. The problem then resolves itself into that of the relation 

 of the germ-plasm to the protoplasm of the rest of the body, the so-called 

 somatoplasm ; and the question to be answered is this : Are variations in the 

 parental somatoplasm capable of inducing such changes in the germ-plasm that 

 somatic peculiarities appear in the offspring similar to those possessed by the 

 parent? Weismann classifies all somatic variations according to their origin 

 into three groups viz. injuries, functional variations, and variations, mainly 

 climatic, that depend upon the environment. The problem of their inherit- 

 ance is a far-reaching one, and upon its correct solution depend principles that 

 are of much wider application than simply to matters of heredity ; for if 

 acquired characters can be inherited, there is revealed to us a most potent fac- 

 tor in the transformation of species, and the whole question of the possibility 

 of use and disuse as factors of evolution is presented. The larger evolutionary 

 problem need not here be considered. 



Regarding the problem of the inheritance of acquired characteristics we may 

 say at once that it is not yet solved. To the lay mind this may seem strange, 

 for at first thought it appears self-evident that parents may transmit to their 

 children peculiarities that they themselves have acquired. Affirmative evidence 

 seems all about us, as witness the undoubted cases of inheritance of artistic 

 tastes, of talent, of traits valuable in professional life, which seem to originate 

 in the industry of the parent. But scientific analysis by Weismann and others 

 of popular impressions, popular anecdotes, and hearsay evidence, and accurate 

 original observation have revealed little that cannot as well be explained on 

 other hypotheses. Anatomical and functional peculiarities of the body that are 

 apparently new often reappear in successive generations, but to assume that 

 they are acquired by the somatoplasm and have become congenital, rather than 



