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Show 1 9 0 3 . ] TRANSPOSITION OF MAMMALIAN TESTES. 331 and the oviduct usually possessing no anatomical connection. How important this is may not only be inferred from a priori considerations, but also from the discovery of the many structural devices adapted to this end. Thus there occurs the " development of special folds of the peritoneum, which practically ensure the passage of the ova into the oviduct when they are extruded from the ovaries. The oviduct, moreover, has a large and fimbriated mouth, called in human anatomy the ‘ morsus diaboli.' This almost wraps round the ovary, and thus prevents the ova from straying in the wrong direction. Moreover, the ovary itself is often so arranged that it can easily be withdrawn into a pocket of the peritoneum, from which the obvious exit is by the gaping mouth of the oviduct. This disposition of the generative parts is still further modified in a few animals, such as the Rat and the Kinkajou. In these animals the mouth of the oviduct actually opens into the interior of a closed chamber which contains the ovary " (Beddard). Thus there exists ample reason for the retentive ligaments usually associated with the mammalian ovary (see Appendix). The Genitalia and Conditions of Locomotion in Ichthyopsida and Sauropsida. If, as we have observed, the conditions of mammalian locomotion alone subject the organisation to those concussive influences which have effected, among other changes, the transposition of the testes ; and if, as we have also seen, only the highest manifestations of terrestrial activity are capable of producing complete testicular descent, then we may be certain that neither in the relatively inactive terrestrial Reptilia, the active aerial Aves, nor the aquatic Pisces will a like phenomenon occur. In Reptilia, though Ophidia and many Lacertilia are capable of brief spasms of great activity, the total impulsiveness is very small and of low degree. This is not only due to general passivity, but also to the fact that " the body of a reptile is, as it were, slung between its limbs like the body of an eighteenth century chariot between its four wheels," with resulting imperfection of the " relations of the limbs to the trunk from the point of view of a terrestrial creature" (Beddard). Apart from the absence of the causal conditions, the depression of the trunk and consequent liability of injury to the testes would in itself have negatived descent (cf. Phocidse above). In the Anura, the only terrestrial amphibia which concern us, adoption of terrestrial habits, resulting in a higher degree of impulsiveness, has as usual for its concomitants structural concentration and increased retentivity or transposition. Here the testes have assumed a " full oval form, compact and undivided : they are situated, as shown in the Frog, on the ventral side of the anterior half of the kidneys" (Owen). That the testes have slightly descended in correspondence with the saltatory |