174 
weismann’s theory of germ-plasm. 
Aug., 1890. 
to which we may come is that, at the time of its deposition, 
the valley extending from Namur to Douai contained but a 
narrow lake, beginning to the west of Mons and ending near 
Tliuilin. There seems to have been a gradual contraction of 
the water-covered area, and consequently of the surface on 
which the coal-forming material was deposited. 
The uppermost position of the cannel coals seems to con¬ 
firm, it is pointed out, the mineralogical classification of coal 
according to the percentage of its gaseous constituents, 
beginning with cannel, the most gaseous and the least altered, 
and ending with the nearly pure carbon of anthracite, the 
oldest of the coals. 
(To be continued.) 
ON WEISMANN’S THEORY OF THE CONTINUITY 
OF THE GERM-PLASM. 
Ever since the publication of “ The Origin of Species,” 
the subject of Heredity has occupied a foremost place in the 
speculations of Biologists, but up to the present no theory 
has been formulated that meets with general assent. Various 
hypotheses have been advanced, but owing to the complexity 
of* the problem, or perhaps to the difficulty of proof, they 
have all remained in the form of provisional hypotheses. 
Darwin, who saw the necessity of attacking the problem, 
devoted to it several chapters of his work on “ Animals and 
Plants under Domestication.” His theory of “Pangenesis.” 
as he named it, presumed that each and every cell of the 
body gave off innumerable particles or gennnules, which, 
flowing from all directions, became concentrated in the 
germ-cells, giving them a complex composition of such 
a character that a single germ-cell could, under proper 
conditions, reproduce every detail of the parent organism. 
Each gemmule exerted its influence on the developing 
germ, and impressed it with the character of the 
cell from which it proceeded. This theory possesses the 
advantage of explaining the transmission of acquired charac¬ 
ters, and the replacement of parts that have been removed 
by injury; a property that is conspicuous among the Reptilia, 
Crustacea, and lower Invertebrata generally. Notwithstand¬ 
ing the weight of the name of its great author, the theory 
has failed to find acceptance on account of the impossibility 
of conceiving how the gennnules are translated from the 
various places where they arise to the germ-cells; it cannot 
be by means of the blood, because, if so, the characters of one 
