1903. ] TRANSPOSITION OF MAMMALIAN TESTES. 335 
to the intensity of the forces concerned, and have thus supplied 
the inductive evidence required to verify the conclusion arrived 
at on & priort grounds. It has also been pointed out that 
transposition of the testes can, from the nature of the function 
of these organs, the mode of emission of their genital products, 
and the absence of adverse external influences, neither cause 
derangements in the individual economy nor impair the fertility 
of the race ; ; and that in consequence of a similar change of 
position in the case of other organs inevitably entailing one or 
other of these penalties, the testes alone have descended. More- 
over, the superior density, the disposition of the attachment, and 
the appropriateness both as regards volume and definiteness and 
concentration of form for change of position, appertaining to the 
testes, lend greater additional facilities to their transposition than 
in the case of other organs not so characterised. Hence we can 
not only show why the testes have descended, but also why they 
alone have thus responded to the incident forces—other or eans, 
for one or more of the reasons supplied, requiring to be m: aintained 
in position by the special retentive structures developed to that 
end. Combining with these facts the additional evidence derived 
from a study of mammalian anatomy, showing that impulsive 
locomotion is not alone responsible for the descent of the testes, 
but that it has also been the prime cause of the evolution of the 
diaphragm, the metanephric kidney, and other minor anatomical 
features, we see still more clearly “ how strong is the probability 
of the theory advanced.” 
Other Illustrations of the Relationship between Visceral Con- 
formation and Impulsiveness : the Evolution of the Diaphragm 
and the Metanephric Kidney. 
Although differmg from the reproductive elements of the body 
as regards their economic relations to the rest of the organism, 
the non-reproductive organs, possessing like material properties, 
may be expected to portray similar structural characteristics in 
relation to locomotor impulsiveness. A consideration of such will 
not only prove of utility as affording indirect confirmation of 
the foregoing, but will provide opportunity for tendering similar 
explanations in the case of other anatomical features. The con- 
stant interrelations of position obtaining between the various 
organs in the vertebrate body are in every case easily accounted 
for, either on mechanical or physiological grounds, and it is 
needless to discuss every organ from these points of view; it will 
suffice if we treat of two or three structural phenomena, the 
interpretation of which is not quite so self-evident or well 
known. 
The complete descent of the testes and the presence of a fully- 
developed diaphragm both being common characteristics of the 
Mammalia, it is possible that the cause to which the former is 
attributable may also suffice to explain the evolution of the latter, 
Proc. Zoot. Soc.—1903, Vor, I. No. XXII. 22 
