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. Evidence 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, i.e. 

 the parents, resemble former ancestors. One or more of the members of a family 

 may, e.ff., 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 is 

 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 



