Professor Schaaffhausen has noticed that many peculiarities of the skull are coincident with arrested cerebral development and correlated to each other:—“The characters observed in the skulls of the lower races, namely, a narrow and low frontal bone, a short sagittal suture, a low temporal squama, a short occipital squama, the upper margin of which forms a flat arch, are therefore to be considered as approximations to the animal form, and they stand to each other in organic connection.”[1588] It seems as if stature and muscular force were in some way connected with the dolichocephalic and the brachycephalic forms of the skull, for Welcker found that short men and short races incline more to the latter, tall men and tall races to the former. Again, according to Fick, the muscles exercise a remarkable influence on the form of the bones in general, and particularly upon some cranial bones.[1589] The process of acclimatization affords opportunities for the study of the connection between organic structures and functions on the one hand, and surrounding nature on the other. At present, however, our knowledge of the subject is exceedingly scanty. It has been asserted that the curly hair of the European becomes straight in America,—like the hair of an Indian; that in North America, as in New South Wales, children of European parents are apt to become tall and lean, whilst there is a tendency among European colonists at the Cape to grow fat,—which reminds us of the steatopygy of the native women.[1590] Almost all that we know with certainty is that, in the process of acclimatization, man has to undergo a change, and that this change is often too great to be endurable. As Dr. Felkin observes, Europeans are almost incapable of forming colonies in the tropics;[1591] and, with few exceptions, they have been unable to rear a sound progeny there in marriage with white women.[1592] Colonel Hadden, who has spent sixteen years in India, informs me that it is a prevalent opinion among British officers in that country that an English regiment of a thousand men would, within thirteen years, from climate, disease, or other casualties, almost wholly die out. This statement well agrees with Professor Sprenger’s, that a regiment consisting of eight hundred men loses within ten years more than seven hundred.[1593] It is also, according to Colonel Hadden, a common report that, of a third generation of pure Europeans in India, children only are, occasionally, met with, and that they never reach the age of puberty.[1594] English parents, as a rule, send their children to Europe when five or six years old, as otherwise they would succumb.[1595] According to Mr. Squier, it is the concurrent testimony of all intelligent and observing men in Central America that the pure whites are there not only relatively but absolutely decreasing in numbers, whilst the pure Indians are rapidly increasing, and the Ladinos more and more approximating to the aboriginal type.[1596]