330 MR. W. WOODLAND ON THE [Apri2i, 
throwing their front parts again forwards. They drag their belly 
along the earth, show little suppleness, and soon become tired.” 
There is no scrotum, the testes being abdominal and “ imbedded 
in areolar tissue.” Thus, as before maintained, the embryonic 
transposition of the testes tends to be checked if external conditions 
become so changed as to render complete descent of these organs 
disadvantageous to the animal, such being obviously the case in 
the Phocidz, which have become further modified for an aquatic 
existence than the Otariide. It may be objected that ordinary 
mammals are subject, though in a less degree, to a like drawback 
—that their testes are also exposed to considerable danger, and that 
on the hypothesis descent ought to have been negatived by natural 
selection, 2.e. by the development of ligaments or supporting 
areolar tissue. Incidentally noting that the actual facts prove 
that no such danger exists, it may be observed that the testes of 
a typical mammal are very efficiently screened, not only laterally 
by their position between the broad thighs of the hind limbs, but 
also posteriorly by the tail; and they are well preserved from 
contact with surrounding objects by the elevation of the body 
upon its limbs, the case being otherwise in Phocide, Cetacea, and 
lower animals. 
The ancestral history and arboreal or other habits of the 
Primates constitute sufficient warrant for the conspicuous exter- 
nality of their testes. ‘That active arboreal habits involve 
impulsiveness of the highest degree, is sufficiently manifest on 
contemplating the movements of any of the ordinary monkeys, 
more especially in the case of the Gibbons. 
Thus in a review of the Mammalia, we encounter a considerable 
mass of evidence testifying to the validity of the theory here 
advocated, and more might be added. In the Monotremata, 
Sirenia, Cetacea, most Edentata, Hyracoidea, Proboscidea, and 
Phocidee, conditions prevail, or have prevailed, negativing the 
descent of the testes; and these conditions have either consisted 
of the absence of that type of terrestrial locomotion which has 
been the sole cause of the transposition of these organs, or of 
secondary factors which have either negatived the operation of 
the primary agency, or effected a reversion of the pre-existing 
effect of the same. 
Since the transposition of the testes is mainly due to their mass, 
and definiteness and concentration of form—their means of 
suspension and physiological separateness from the body merely 
constituting conditions to the transposition—it follows that the 
small and diffuse ovaries of the Mammalia will not respond in 
any degree to the forces incident on the body, the magnitude of 
the strains on an attachment obviously being proportional to the 
mass of the organ attached. But apart from the smallness of 
mass possessed by the ovaries, there exists an important reason 
for their retention at or near the primitive position i the body- 
cavity. This reason is the necessity of the proximity of the ovary 
to the oviducal aperture for the conservation of the ova, the ovary 
