PACKARD. — INHERITANCE OF ACQUIRED CHARACTERS. 333 



In 1887 Minot* in a brief note suggested that Niigeli's hypothetical 

 idioplasm is probably identical with the nuclear chromatin of mor- 

 phologists ; and that heredity is due to the transfer from parent to off- 

 spring of the nuclear substance. 



Maupas,f in two memoirs published in 1889 and 1890, reaffirmed 

 and extended this view, concluding that the chromatin of all cells is 

 the bearer of heredity. 



Meanwhile in 1885 appeared Weismann's epoch-making essays on 

 heredity, his view being somewhat in the line of Jaeger's theory, 

 but greatly expanded, and with many new and original suggestions. 

 He stated that it was impossible to prove the existence of gemmules, 

 and substitutes for pangenesis the now famous doctrine of " the con- 

 tinuity of the germ plasm," as affording a more rational basis than 

 pangenesis or Brooks's modification of it. Weismaun says : " The 

 nature of heredity is based upon the transmission of nuclear substance 

 with a specific nucleoplasm of the germ cell, to which I have given 

 the name of germ plasm" (p. 180). As stated by Mr. E. B. Poulton,J 

 an able commentator and exponent of Weismann's views, — 



"The word 'continuity ' expresses the theory that heredity depends 

 on the fact that a minute quantity of this germ plasm is reserved 

 unchanged during the development of the individual, and afterwards 

 grows and gives rise to the germ cells. Hence the germ plasm is 

 continuous from one generation to another in an unending succession, 

 and from it the germ cells of each generation are produced. 



" Parent and offspring resemble each other because both arise from 

 the same substance, which develops rather later in the case of the 

 offspring. Hence everything which is predetermined in the germ cell, 

 every blastogenic character, may be transmitted, while somatogenic 

 characters cannot be transmitted." 



We will quote Weismann's definition of acquired and blastogenic 

 characters : " We maintain that the ' somatogenic ' characters cannot be 

 transmitted, or, rather, that those who assert that they can be trans- 

 mitted must furnish the requisite proofs. The somatogenic characters 

 not only include the effects of mutilation, but the changes which follow 



* Science, New York, VIII. 125. 



t Sur la Multiplication des Infusoires Cilie's. Archiv de Zoologie expe'rimen- 

 tale, se'r. 2, VI. 165-273; Le Rajeunissement Knryogamique chez les Cilie's, 

 VII. 149-517. See also Hartog, Quart. Journal Microscop. Science, December, 

 1891, and Osborn, loc. cit., pp. 54-56. 



\ Theories of Heredity. Reprinted from the Midland Naturalist, November, 

 1889. 



