Some years ago certain naturalists were wont to maintain that plants and animals had reached their present stage of development through the operation of internal (innate) forces. Now, however, the belief is all but universal that organisms are what they are to-day because of the operation of external forces - that they have reached their present stage through the ever-present influence from generation to generation of the external surroundings or environment. If, during the past, the environment (which includes not only the food, temperature, and other like influences, but also the influence living things have on each other) has been the means of producing so marvellous results - of not only causing variation but also of playing the part of the selector, - it may be safely assumed that changes in the external conditions may even in a single lifetime lead to very decided modifications - not necessarily of a permanent (hereditary) kind - in, say, the size and fitness, the time at which maturity is reached, and more especially in the germ-cells from which the next generation springs.

That in the case of the horse the external conditions or environment count for something, a glance at the history of the Equidoe affords sufficient evidence. In early Eocene times the representatives of recent horses were small-brained, primitive, five-hoofed creatures, about the size of a wolf, but at the most semi-plantigrade. As age succeeded age the outer digits (1 and 5) gradually dwindled, and at length Hipparion appeared on the scene, a creature decidedly equine in form, and only essentially differing from the horse of to-day in its teeth and in its limbs, each limb bearing three complete hoofs, as in the rhinoceros.

At a still later period the evolution of the horse was carried a stage further by the shrinking within the skin of the second and fourth digits, already quite useless in Hipparion and in the three-toed horse (Proto-hippus) of the New World.

Like Hipparion (many fossils of which have been unearthed near Athens), the true horse, during at least the Reindeer period in Europe, was of a considerable size. This conclusion is supported by the size of the petrified remains in the Rhone valley, where for a time the horse afforded abundant sport for Palaeolithic man. Just as in olden times the elephant in certain areas dwindled in size to form pigmies measuring sometimes only 36 inches, so the horse gradually dwindled to form certain pigmy breeds which (as in the Shetland Islands) were often as small as the little elephants that in olden times flourished in what is now the Island of Malta.

1 By Professor Cossar Ewart in the Live Stock Journal Almanac.

In the case of the horse, as in the case of the elephant, the dwarfing was undoubtedly due to unfavourable surroundings. If the external conditions were sufficient in, geologically speaking, a comparatively short time to dwarf the horse until it was actually smaller than the " fossil horses" of the remote Eocene epoch, it is not surprising that man - with his wonderful control over nature - is able even in a single generation to modify greatly the horse and other domestic animals. That in a few centuries the large, highly-nervous race-horse, with his wonderful speed and courage, has been evolved out of Eastern and native ponies is a matter of history, and everybody knows that while some are now engaged in breeding pigmy horses little over 30 inches in height, others are as successfully breeding huge, powerful animals as wonderful in their way as their pigmy relatives. It may even be said that a recognized part of the breeder's work consists in modifying, through changes in the external conditions, the animals to which he happens to devote his special attention, just as horticulturists, by food, heat, and timely shelter, alter plants until all resemblance to their wild stock is as good as lost.

Breeders of Shetland and polo ponies, and, for that matter, breeders of race and heavy horses, know well enough that to have any chance of success they must exercise the utmost vigilance over the conditions under which their foals, colts, and fillies are reared. Hitherto, as far as I can learn, breeders have not had at their disposal any very accurate information as to the rate of growth of horses either during development or after birth, and hence, though aware that growth is rapid during the first year, they have been without any certain index as to when changes in the food, temperature, etc, are likely to produce the maximum effect.

Having for some years been collecting data bearing on the development and rate of growth of the horse, I propose now placing on record such facts as are likely to prove interesting and suggestive to breeders, and to lead, perchance, to the influence of various kinds of treatment before and after birth being systematically investigated. In studying the rate of growth of the horse, it is hardly necessary to point out that on the one hand allowance must be made for the influence of the external conditions, and on the other for hereditary influences, i.e. the stereotyped changes ultimately due to the environment. In other words, that in an investigation of this kind the surroundings should be as natural as possible, while the animals used should neither be characterized by an hereditary tendency to produce either very large or very small offspring. Bearing these points in mind:

1 selected for observation the offspring of horses from 14 hands to 14 hands.

2 inches in height - the height at times reached by horses living in an almost wild state in the west of Ireland- - and I provided the foals and colts under observation with as natural surroundings as circumstances permitted.

Having fixed on the size of the horses to be studied, it was next necessary to consider how the rate of growth before and after birth could be best determined.

The difference between a tall and an undersized man is mainly a difference in the length of the legs; but in the case of the horse the height, as commonly understood, instead of bearing, as in man, an intimate relation with the length of the hind-limbs, is intimately related to the length of the fore- limbs.