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Show 1 9 0 3 . ] TRANSPOSITION OP MAMMALIAN TESTES. 321 its members exhibit, and by the more perfect adaptation of the body (relation of limbs to trunk, &c.) to the locomotion in which the superior activity is mainly manifested. Consequently, in mammals, the reactions which occur between the organism and the substratum vastly exceed in magnitude those occurring in lower groups, and we have in this distinction a factor which in considering bodily conformation is worthy of all attention. Since in mammals the organisation is subject to such considerable forces, it follows that if stability of position be required in connection with organs possessing appreciable mass, i. e. if these organs are to adjust themselves to those transposing influences which arise out of impulsiveness, fixative structures must be developed in response to the demand. For, as remarked above, a sudden acceleration imparted to the body is necessarily transmitted to an attached organ through its attachment, which, if the organ be of considerable mass, is thereby subjected to an intense strain, possibly ending in disruption. Stability of position of an organ may be necessitated either on mechanical or physiological grounds: thus, apart from considerations of function, viscera of large mass (stomach, liver, intestine) must conform, as regards situation in the body-cavity, to the principle that, cceteris paribus, the more anterior the centre of gravity of the body the greater the facility of progression1; and again, from the functional standpoint, the kidneys must in active animals be maintained anteriorly in order to ensure proximity to a vigorous blood-supply. It will be evident from this, that if the position of an organ be of no economic moment-if there be no need of localisation either on account of mass or volume for preservation of bodily equilibrium, or on account of nature of function for physiological efficiency,- retentive structures will not tend to be formed, and the organ, if of sufficient mass, will respond by transposition to any considerable force incident upon it-a trait which in the course of generations will be inherited. I shall now proceed to examine more in detail the production of the forces hitherto assumed to be capable of effecting the transposition of the testes-to enquire whether the intensity and direction of these forces are such as are congruous with the hypothesis advocated. Mammalian Locomotion. In view of the importance that is here attached to the character of mammalian locomotion, it is needful to discuss the subject in detail. Every unsupported mass descends to the earth with a given acceleration, and the magnitude of the force required to re-elevate the body to its initial position is directly proportional 1 Well shown bjr measurements of the position of the centre of gravity in Pisces, and by the abdominal contours of active cursorial mammals as compared with those of species more slothful in habit (compare e. g. a greyhound or race-horse with a St. Bernard or cart-horse, or, more generally, herbivores with carnivores, though the different capacities of the digestive organs have here to be considered). 21* |
