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Show 330 MR. W. WOODLAND UN THE [Apr. 21, throwing their front parts again forwards. They drag their belly along the earth, show little suppleness, and soon become tired." There is no scrotum, the testes being abdominal and " imbedded in areolar tissue." Thus, as before maintained, the embryonic transposition of the testes tends to be checked if external conditions become so changed as to render complete descent of these organs disadvantageous to the animal, such being obviously the case in the Phocidse, which have become further modified for an aquatic existence than the Otariidse. It may be objected that ordinary mammals are subject, though in a less degree, to a like drawback -that their testes are also exposed to considerable danger, and that on the hypothesis descent ought to have been negatived by natural selection, i. e. by the development of ligaments or supporting areolar tissue. Incidentally noting that the actual facts prove that no such danger exists, it may be observed that the testes of a typical mammal are very efficiently screened, not only laterally by their position between the broad thighs of the hind limbs, but also posteriorly by the tail; and they are well preserved from contact with surrounding objects by the elevation of the body upon its limbs, the case being otherwise in Phocidae, Cetacea, and lower animals. The ancestral history and arboreal or other habits of the Primates constitute sufficient warrant for the conspicuous externality of their testes. That active arboreal habits involve impulsiveness of the highest degree, is sufficiently manifest on contemplating the movements of any of the ordinary monkeys, more especially in the case of the Gibbons. Thus in a review of the Mammalia, we encounter a considerable mass of evidence testifying to the validity of the theory here advocated, and more might be added. In the Monotremata, ►Sirenia, Cetacea, most Edentata, Hyracoidea, Proboscidea, and Phocidae, conditions prevail, or have prevailed, negativing the descent of the testes; and these conditions have either consisted of the absence of that type of terrestrial locomotion which has been the sole cause of the transposition of these organs, or of secondary factors which have either negatived the operation of the primary agency, or effected a reversion of the pre-existing effect of the same. ►Since the transposition of the testes is mainly due to their mass, and definiteness and concentration of form - their means of suspension and physiological separateness from the body merely constituting conditions to the transposition-it follows that the small and diffuse ovaries of the Mammalia will not respond in any degree to the forces incident on the body, the magnitude of the strains on an attachment obviously being proportional to the mass of the organ attached. But apart from the smallness of mass possessed by the ovaries, there exists an important reason for their retention at or near the primitive position in the body-cavity. This reason is the necessity of the proximity of the ovary to the oviducal aperture tor the conservation ot the ova, the ovary |