190 
determination, and significance of the 
polar bodies. Between 1880 and 1883 
he was engaged in his epoch-making 
researches on the germ-cells of hydroids 
which uncovered the fundamental facts 
on which his theory of the continuity of 
the germ-plasm was based. 
The special papers and memoirs deal- 
ing with these and other investigations 
constitute a great body of knowledge to 
which zoologists will constantly refer as 
the foundation of many important lines 
of research. 
About 1884 he was forced to turn from 
such investigations, owing to increasing 
eye troubles. From this time date those 
contributions to the theory of evolution 
and heredity for which he is best known 
to the general educated public, as one of 
the greatest of Darwin’s successors. 
These were however by no means his 
first publications on these subjects, for 
in 1868 he had published a “ Justifica- 
tion of the Darwinian Theory,” in 1873 
a study of the influence of isolation in the 
origin of species, and a volume of studies 
on the theory of descent, later translated 
into English. 
His best-known contributions on these 
subjects began with a series of essays 
published between 1881 and 1891 on the 
“Duration of Life”? (1881), on ‘ Hered- 
ity’ (1883), “Life and Death” (1883), 
“The Continuity of the Germ-plasm as 
the Foundation of a Theory of Hered- 
ity’ (1885), “ The Significance of Sexual 
Reproduction in the Theory of Natural 
Selection ’’ (1886), ete., ete., all of which 
led up to and culminated in his volume 
on The Germ-plasm (1892). In 1896 his 
Germinal Selections appeared. In 1902 
all of his theoretical considerations were 
brought together in two volumes on, The 
Evolution Theory, translated by Professor 
and Mrs. J. Arthur Thompson in 1904. 
It is impossible to discuss in any full- 
ness the theories of these publications. 
THE AMERICAN MUSEUM JOURNAL 
All centered around his conception of the 
continuity of the germ-plasm, and of 
heredity as developmental recapitula- 
tion; thus the denial of the prevalent 
belief in the inheritance of acquired 
characters was a necessary corollary of 
this conception of inheritance. Weis- 
mann maintained not only that the in- 
heritance of variations and mutilations 
of somatic origin was theoretically im- 
possible, but he labored to show that it 
was by no means a necessary support of 
the evolution theory, as had been gener- 
ally assumed. He met with greatest 
skill and keenest logic the many attacks 
which followed the statement of his 
position; his controversy with Herbert 
Spencer on this subject between 1893 
and 1895 constituted the most notable 
of these debates. In the end he com- 
pletely won over the great majority of 
to his way of thinking, 
and freed the theory of evolution and 
heredity from an enormous incubus. 
In his theory of the continuity of 
the germ-plasm, Weismann formulated a 
point of view on which all subsequent 
genetic research must be based. He 
recognized with Darwin that a theory 
of evolution must find its final analysis 
in the life history of the individual, 
which contains the key to heredity and 
variation. Darwin’s theory of pangene- 
sis, constructed as a formal hypothesis 
of heredity and variation, involved un- 
naturalists 
necessary and untenable conceptions; 
he had assumed that each cell of the 
body produced, at all stages of its life, 
living particles (gemmules) capable of 
reproducing the parent cells. These 
particles were cast off from the parent 
cells and accumulated in the germ-cells, 
each of which was supposed to contain a 
complete assortment arranged in a 
definite fashion. The development from 
the germ-cell depended on the successive 
liberation and development of these 
