1883.] Recent Literature. 1263 
tempts to show that it is supported by direct proof, and the work 
closes with an extended statement of the theory. 
Professor Brooks’ theory we wilt state in his own words : 
“The union of two sexual elements gives variability. Conjuga- 
tion is the primitive form of sexual reproduction. Here the func- 
tions of the two elements are alike, and the union of parts derived 
from the bodies of two parents simply insures variability in the 
offspring. In all multicellular organisms the ovum and the male 
cell have gradually become specialized in different directions. _ 
“The ovum is a cell which has gradually acquired a compli- 
cated organization, and which contains material particles of some 
kind to correspond to each of the hereditary characteristics of 
the species. The ovum, like other cells, is able to reproduce its 
like, and it not only gives rise, during its development, to the 
divergent cells of the organism, but also to cells like itself. The 
ovarian ova of the offspring are these latter cells, or their direct 
unmodified descendants. ‘ 
“Each cell of the body is, in a morphological sense, an inde- 
pendent individual. It has the power to grow, to give rise, by 
division, to similar cells, and to throw off minute germs. During 
the evolution of the species it has, by natural selection, acquired 
distinctive properties or functions, which are adapted to the con- 
ditions under which it is placed. So long as these conditions 
remain unchanged, it performs its proper functions as a part of the 
body; but when, through a change in its environment, its func- 
tion is disturbed and its conditions of life become unfavorable, it 
rows off small particles which are the germs or ‘gemmules 
of this particular cell. 
“These germs may be carried to all parts of the body. They 
May penetrate to an ovarian ovum or toa bud, but the male a 
has gradually acquired, as its special and distinctive function, a 
Peculiar power to gather and store up germs. or 
“When the ovum is fertilized each germ or ‘ gemmule perar 
with, conjugates with or impregnates that particle of the ovum whic 
is destined to give rise in the offspring to the cell which ee 
sponds to the one which produced the germ or gemmule; or cise 
£ unites with a closely related particle, destined to give rise ere 
Closely related cell. 
“When this cell becomes developed in the body of the off- 
Spring it will be a hybrid, and it will therefore tend to vary cen 
“ As the ovarian ova of the offspring share by direct inae hich 
all the properties of the fertilized ovum, the organisms seyi 
they ultimately give rise will tend to vary in the same m gem- 
“A cell which has thus varied will continue to throw olf ge 
Mules, and thus to transmit variability to the corresponding oe 
in the bodies of successive generations of descendants un 
vorable variation is seized upon by natural suse ona lected will 
‘As the ovum which produced the organism vfaguetnen 
