THEORY OF EVOLUTION. 
Gen. Sub. 11 
°Weismann, A. Ueber den Riickschritt in der Natur. Ber. Freiburg 
Ges. ii. pp. 1-30. 
. Die Bedeutung der Sexuellen Fortpflanzung fur die Selections- 
Theorie. Jena : G. Fischer. (Summary by H. N. Moseley, Nature, 
xxxiv, pp. 629-632.) Cf. Die Continuitat des Keim-plasmas, &c., 
1885. 
Main theme — the importance of sexual reproduction as a moment in 
evolution. Special new characters acquired by the Metazoan parent in 
response to environmental influences are not known to be hereditarily 
transmitted to offspring. On the theory of the continuity of the germ- 
plasma, the molecular constitution of the germ -plasma is already deter- 
mined within the embryo. It grows enormously in quantity, but retains 
its original structure persistently, not directly influenced by environment, 
which cannot therefore originate variations. Sexual reproduction, as the 
mingling of two different sets of hereditable tendencies, supplies the mate- 
rial for the development of individual variations, out of which selection 
produces new species. It does not obliterate, but sums up the minute 
individual differences. The prepotency of the various kinds of idio- 
plasm which compose the germ- plasma of the germ-cells of each indi- 
vidual must vary in intensity at various periods of life. Hereditarily 
transmissible variation having arisen in the Protozoa by the direct action 
of external conditions, is retained in the Metazoa , and enhanced by ever 
changing combinations in sexual reproduction. The primitive action and 
meaning of conjugation is a strengthening of the forces of the organism 
in relation to reproduction, and does not imply rejuvenescence. It after- 
wards becomes a source of variability. A species parthenogenetieally 
reproduced must be nearing its extinction ; superfluous organs do not 
become rudimentary in such species. 
^Wigand, A. .Grundsatze aller Naturwissenschaft. Marburg : -/6, 
35 pp. 
0 Wilson, A. S. The Survival of the Fittest. A. Gardner. 
°Worsley-Benson, H. S. Charles Darwin. Bath : 8vo. 
Cf ZECHA, A. .Versuche mit der Truthiihnerzucht auf Racebildung. MT. 
orn. Yer. Wien (10) xxiv, pp. 284-287. 
2 . Variation. 
Beddard, F. E. Variations in Perionyx excavatus. P. Z. S. pp. 308-^314, 
4 figs. 
Fifteen variations in position and number of genital pores, &c. 
c Outler, E. Probable Cause of some Monstrosities : the Abnormal 
Forms of Spermatozoa. Medical World, iv, pp. 18-20 ; J. R. Micr. 
Soc. vi, p. 58. 
°Dall, W. H. [See Evolution (1).] 
The greater number of similar members or parts, the greater the ten- 
dency to vary (1) in the minor features, and (2) in the number per indi- 
vidual as compared with average number for species. In deep-sea the 
