376 Ewart— Variation: Germinal and Environmental. 
6. The offspring of half-breeds are, as a rule, extremely variable—a fact 
long recognised by breeders, fanciers, and horticulturalists. Half-wild rabbits 
are surprisingly uniform in their colour, size, time of reaching maturity, &c., 
yet when interbred, even if closely related, they produce highly varying 
offspring. EKvidence of this we have in the litter of eight already referred 
to, the members of which differed in every possible way—in structure, colour, 
size, weight, disposition and habits, vitality, time of reaching maturity, and in 
the preparations made for, and the care taken of, their young. What is 
true of rabbits is more or less true of mice, pigeons, and of many other 
animals, and of plants, more especially of plants in which cross-fertilization 
does not ordinarily occur. In orchids, as in rabbits and mice, first crosses 
are uniform in their characters, but when the first crosses are interbred, varia- 
tion at once sets in, some resembling the parent species, others the immediate 
parents, while others form a series of links between the parents and the 
less remote ancestors, or differ from all the known ancestors. This ‘“‘ sporting ” as 
it is often called, may continue for several generations, but it eventually subsides 
as the potency of one particular variety is fixed by inbreeding. ‘The epidemic of 
variation that often sooner or later result from intercrossing, followed by inter- 
breeding, seems to be partly due to the mixing-up of two kinds of germ-plasm 
having different tendencies, partly to an increase of vigour induced by intercrossing. 
Every variety and species in a state of nature in order to survive, must, on the one 
hand, be capable of varying with its ever-changing surroundings, but, on the other 
hand, to prevent waste, it should not at any given time vary too much. Excess of 
variation is checked by inbreeding, which often, for economical reasons, is as great 
as the vigour of the variety or species permits. But, for inbreeding, the members 
of a species would probably be too sensitive to external stimuli. When the 
‘‘ constitution ” is broken down by intercrossing the influence of the environment 
—food, temperature, &c.—seems to reach a climax. The characters of the 
secondary and tertiary and other crosses still depend on what happens during 
conjugation (germinal variation), but this is apparently influenced to an unusual 
extent by the condition of the parents, the nutrition and ripeness of the germ- 
cells, and especially by the retrogressive changes in the ova after the ‘‘ reducing 
division.” 
7. Sometimes the offspring, instead of resembling the immediate ancestors, @.e. 
the parents, resemble former ancestors. One or more of the members of a family 
may, ég., resemble a grandparent, or a comparatively remote ancestor, or one of 
the intermediate ancestors. Whether, in any given case, the resemblance to a 
former ancestor is due to retrogressive variation (reversion or regression), it 1s 
impossible to say. Nevertheless, in most cases, a fairly satisfactory answer can be 
given. When the offspring all but exactly agree with a grandparent or even a 
