326 MR. W. WOODLAND ON THE Apr. 21 
if ) 
orders and families of the Mammalia affords such conclusive 
evidence as to the causal relation subsisting between the two 
that a systematic review of this evidence is well called for. That 
the correspondence is not absolute, however—that there exist 
instances of the concurrence of scrotal testes with sluggish habits 
—is without doubt mainly, if not wholly, to be explained by 
phylogenetic considerations. For it must be remembered that 
once the descent of the testes is inherited, the trait is a constant 
one (unless acquired sluggishness is able in time to produce effect, 
which is doubtful), and remains so in successive generations 
whatever varied habits may be assumed, unless the bionomic 
aspect so changes that natural selection cancels the ‘ plus varia- 
tions,” so affording an ascendancy to reversionary factors. That 
such has been the case in several instances will be illustrated 
below. 
In the Monotremes the activity (impulsiveness) is of a very 
low degree. Ornithorhynchus is “aquatic in its habits, passing 
most of its time in the water or close to the margin of lakes and 
streams.” The ‘ body is rather long, compact, and almost every- 
where of the same thickness. It rests on short, massive legs 
......80 short that the animal in walking or running actually 
drags its body along the ground.” Hchidna is “ usually found in 
rocky districts, and more especially in the mountains...... and 
is mainly of nocturnal habits.” It is described as ‘“ indolent.” 
The testes in both instances are ‘abdominal in position through- 
out life,” and afford the only example in mammals of a disposition 
of these organs anterior to the kidneys. The low status of these 
animals is well known. 
Inthe Marsupials “ the testes are always contained in a scrotum, 
which is suspended by a narrow pedicle to the abdomen in front 
of the penis.” If it is permissible to assume that the ancestor of 
the marsupials was kangaroo-like, the pre-penial position of the 
testes may perhaps be attributed to the peculiar mode of loco- 
motion characterising this animal. For the rapid locomotion of a 
Kangaroo consists of a series of leaps, and such leaps would involve, 
ag in ordinary mammals, a series of antero-dorsal tensions on the 
suspensory membranes of the testes; but since the bodily depres- 
sions are marked by a more prolonged termination, as compared 
with those involved in the ordinary gallop, the testes would in 
addition tend to be thrown: forward, and these two factors in 
conjunction have possibly led to the peculiar position of the testes 
found in marsupials. On no other theory than that of descent 
from an ancestor characterised by pre-penial testes can the peculiar 
genital conformation of the variously habited marsupials be corre- 
lated with special bionomic conditions; and hence, on this ground 
alone, it is possible, as implied above, that the ancestor of the 
Marsupialia was of the type of the Macropodidee, the characteristic 
saltatory progression originating the pre-penial situation of the 
scrotum in the manner indicated. 
The Edentata represent another ancient group. Their activity 
