Notices of Books « 
^October, 
we ask, why have the two sexes been developed ? Mr. Darwin 
finds the answer in the fad that the offspring of two distinct 
parents, especially if descended from stocks exposed to some- 
what dissimilar conditions, have an advantage in vigour over the 
progeny of a single self-fertilised individual. But if, as appears 
probable, the sexes were primordially separate, why did they 
become blended into hermaphrodite forms, and why — in all the 
higher animals and in some plants — have the sexes again been 
separated ? The bilateral strudture of animals, as Mr. Darwin 
suggests, perhaps indicates that they were aboriginally formed by 
the fusion of two individuals. In connection with this subjedt 
we have had occasion to refer to certain curious cases of bilateral 
hermaphroditism found among moths, where one wing, antenna, 
&c., bear the characters of the male, whilst the other side is as 
plainly female. But we have vainly sought for any analogous 
instance either among other inseCts or among birds and 
mammals. 
The whole tendency of these researches, when calmly and 
impartially weighed, must be to shake the confidence commonly 
felt in the primordially distinct character of “ species ” as com- 
pared with mere varieties. The difference in the affinities of the 
sexual elements of different species, on which their mutual inca- 
pacity for breeding together depends, is caused by their having 
been habituated for a very long period each to its own conditions 
and to the sexual elements having thus acquired firmly fixed 
affinities.” 
The Various Contrivances by which Orchids are Fertilised by 
Insects. By Charles Darv/in, F.R.S. Second Edition, 
Revised. London: John Murray. 
This work is already too widely and too favourably known to 
require examination or comment. The present edition has been, 
as the author informs us, enriched with many new and curious 
fads communicated by correspondents in different parts of the 
world, among whom especial mention is made of Dr. Fritz 
Muller. A few errors have also been corrected. We cannot 
help regarding it as a somewhat unfortunate omission that the 
author has not given a list of the additions and modifications 
introduced into the present edition. It must, however, be dis- 
tinctly understood that the alterations thus made are far from 
invalidating the conclusions reached in the former edition. A 
list is appended of all the memoirs and books bearing on the 
fertilisation of the Orchidese which have appeared since the first 
appearance of the present work, in 1862. It is somewhat sin- 
gular that, whilst the botanists of England, America, Germany, 
and Italy have laboured diligently in the investigation of this 
