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Show 1 9 0 3 . ] TRANSPOSITION OF MAMMALIAN TESTES. 3 2 7 in general is small. The Bradypodidse are arboreal in habit, and are characterised by " habitual sluggishness," being " most inefficient walkers," and in climbing, never leaping from bough to bough (a form of activity involving more impulsiveness than even the gallop, but probably not more than that involved in saltation). Their testes are placed close to each other, lying on the rectum between it and the bladder; i. e. are retained in the abdomen. The Myrmecophagidse are also not noted for activity, and their testes are disposed as in the Sloths. The Dasypodidse are similarly inactive, being " harmless and inoffensive," endeavouring to escape by rapid burrowing. However, it is stated that " they can run with great rapidity." The testes are a,bdominal, lying " above the brim of the pelvis." The Manidse are terrestrial and burrowing in habit, but some members of the group can climb trees. They are not very active. The testes lie in the inguinal canal. The Orycteropodidae (Aard-varks or African Ant-eaters) are terrestrial and fossorial. Their testes are " inguinal, but they appear to descend, at all events temporarily, into a scrotum." Their phylogenetic position is uncertain. In the order Sirenia the testes, needless to say, are abdominal. These animals are " slow and inactive in their movements, mild, inoffensive," browsing at the bottom of water. The piscine locomotion of the Cetacea sufficiently accounts for the abdominal position of their testes, which organs are placed in the proximity of the kidneys. Even assuming the terrestrial ancestor of the Cetacea to have been characterised by the externality of the testes (which is improbable considering their existing localisation), such would inevitably have assumed an internal position consequent on the serious risk of injury involved under Cetacean conditions. The Rodents are comparatively small animals. In habit they are mostly terrestrial, but some are arboreal and some natatorial. " The testes in the rutting-season form projections in the groins, but (except in the Duplicidentata) do not completely leave the cavity of the abdomen," i. e. the scrotal elevations are not well-defined. The Duplicidentata comprise the Hares, Babbits, and the Picas or Tailless Hares, all extremely active animals, the latter being described as " agile " and as living in crevices among rocks. The Simplicidentata comprise the remaining Rodents, the principal families of which are the following :- The Sciuridse " vary between the two extremes presented by our ordinary squirrels, the agile climbers, and the sluggish, clumsy marmots, which live almost entirely underground." Assuming the statement to be correct that the condition of the testes is similar in each of these two divisions (which is doubtful), it is evident that the latter are specialised forms descended from active ancestors. The locomotion of the Di pod id ye resembles that of the marsupial Macropodidse and insectivoran Macroscelidse. " The w'hole structure is adapted for jumping, and we find resemblances in their structure on the one hand to the kangaroos, and on the other |
