not a gallop. The Anura among the Amphibia are saltatory, but their leaps
are usually single, or repeated only a few times, not sustained gallops.
The exceptions among the Mammalia still more tend to prove the close
correspondence between the 'impulsive' mode of progression and the
dislocation of the male gonads. In the Monotremata there is no scrotum,
the testes are in a position similar to that which obtains in Reptiles,
and they are the only Mammals in which these organs are anterior to the
kidneys. In locomotion they are sluggish, there is no running or galloping
among them. _Ornithorhynchus_ is aquatic in its habits, and _Echidna_ is
nocturnal and moves very slowly. In Marsupials the scrotum is in front of
the penis, but really in the same position as in other Mammals--that is,
in front of the ventral part of the pelvic girdle. It is the penis which
is different, as the skin around the organ has not united in a ventral
suture below it, while the organ itself has not grown forward adnate to
the abdominal skin as in most other Mammals. The scrotum is always
anterior to the origin of the penis, although in the Eutheria apparently
behind that organ. The larger Marsupials like the kangaroos are eminently
saltatory, and the others are active in locomotion. The aquatic Mammals
Sirenia and Cetacea have no scrotum, the testes being abdominal. It is
unnecessary to inquire whether this is the original position, or whether
they are descended from ancestors which had a scrotum: in either case the
position of the testes corresponds to the absence of what Dr. Woodland
calls impulsiveness in progression. The Fissipedia offer an instructive
example, for while the Otariidae have the hind feet turned forward and can
move on land somewhat like ordinary Mammals, the Phocidae cannot move
their hind legs independently or turn them forward, and can only drag
themselves about on land for short distances. In the former the testes are
situated in a well-defined scrotum, in the latter these organs are
abdominal. The Phocidae are probably descended from Mammals of the
terrestrial type with a scrotum, which has disappeared in the course of