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Show 324 MR. W. WOUDLANl) ON TIIE [Apr. 21, to the rest of the body. If an organ be imbedded or otherwise firmly affixed to the main bulk, it will 011 account of its large area of attachment and close apposition readily share both the elevations and depressions incurred in locomotion-the strains and stresses are distributed in space and time, and hence their intensity is lessened; if, on the other hand, a massive organ be merely suspended from the main mass of the body, such a condition subjects the attachment to the influence of severe strains periodically recurring, the direction of which approaches that of the resultant acceleration of the trunk during its impulsive elevation. The great severity of these strains on the attachment of an organ thus disposed will be more fully realised if it be remembered that, on the sudden elevation of the body, the organ possesses the downward velocity due to the previous depression-a momentum which in being destroyed throws additional strain on the means of support. As will be seen, the preceding remarks apply in an eminent degree to the testes. The Genitalia of Mammalia. The reproductive organs of the Mammalia are relatively small bodies of great density and, in the case of the males, compactness, and they primitively occupy a position similar to that found in the lower Vertebrata. It is, however, characteristic of the majority of the Mammalia that in the course of development the testes forsake their primitive lodgment, and migrate posteriorly and ventrally to the terminal periphery, where they protrude at the surface of the body-wall. This protrusion constitutes the scrotum, in the wide sense of the term, which may vary in character from that of a pair of small slightly-elevated areas to that of a capacious oval pedunculated sac. Apparently in man alone the section of the coelom contained within the scrotum becomes completely separated oil* from the main cavity; in other mammals, communication is retained by means of the inguinal canal, which, however, is usually narrow, so negativing return of the testes to the main body-cavity. This feature in the case of active mammals possessing large testes is very important, since if the unattached organs were permitted to return to the main cavity, the forces to which they would be exposed during locomotion would doubtless be exceedingly detrimental-a malinfluence which both the narrowing of the inguinal canal and the possible tractive function of the gubernaculum during development safeguard against. I11 fact, contrary to the usual supposition, the internal and not the external situation of the testes is the source of danger. It will also be observed that in small animals which do not possess narrow inguinal canals, there is no such dire necessity for the restriction of the testes to the scrotal cavity, both on account of the smaller size of the organs and the usually less intense forces to which the testes are subjected. Thus, paradoxical as it may seem, the increased protrusion of the testes |
