192 The American Naturalist. [March, 
and marrow of the first edition of the ‘Origin of Species.’ And 
what the evolutionist stands in need of just now is not an itera- 
tion of the fundamental principles of Darwinism, but some light 
upon the questions, What are the limits of variation? and, If a 
variety has arisen, can that variety be perpetuated, or even intensi- 
fied, when selective conditions are indifferent, or perhaps unfavor- 
able, to its existence? ” 3 
Thus, twenty years ago, Huxley declared Evolution well estab- 
lished, with the Law of Natural Selection as one of its well- 
determined factors, while he found that we were merely upon the 
threshold of knowledge of the laws of Variation. Some sanguine 
biologists of to-day believe we have crossed this threshold in the 
patient researches of the two intervening decades; but others are 
represented by Professor Lankester, who has now taken the rank 
of leading English critic, and has recently summed up our 
knowledge in an article‘ presumably written with the greatest 
care and deliberation, as follows: 
“ Their causes (7. e., the causes of variations) are extremely diffi- 
cult to trace in detail, but it appears that they are largely due to a 
“shaking up” of the living matter which constitutes the fertilized 
germ or embryo-cell, by the process of mixture in it of the sub- 
stance of two cells—the germ-cell and the sperm-cell—derived 
from two different individuals. Other mechanical disturbances 
may assist in this production of congenital variation. Whatever 
its causes, Darwin showed that it is all-important. . 
Hence there is no necessity for an assumption of the papai 
of direct adaptations.’ The selection of the fortuitously (fortui- 
tously, that is to say, so far as the conditions of survival are con- 
cerned) produced varieties is sufficient, since it is ascertained that 
they will tend to transmit those characters with which they them- 
selves were born, although it is of ascertained that they could» 
transmit characters acquired on the way through life.” 
* He then observes that Mr. Darwin formerly inclined to answer these questions in the 
rere but latterly in the affirmative. 
“ The History and Scope of Zoology.” Enc. Brit. Vol. XXIV. Also “ Advancement 
me Science,” pp. 372-73. 
53. e., of acquired characters. 
