286 The American Naturalst. [March, 
subsequent to which the permanent, commonly described descent 
takes place. 
The anatomical relations in the marsupialia, carnivora and ungulates 
are to be regarded as indicating a separate line of divergence of these 
groups from the rodent-like conditions. The position of the scrotum 
is not really so aberrant in the marsupial as to interfere with close 
comparisons. 
A preformed scrotum is here again to be regarded as a falsification 
of the phylogenetic history, associated with the permanent establish- 
ment of the descent in the embryonic period. 
From numerous facts, of which I have given an imperfect survey 
above, the author establishes a connection between the mammary 
eee and the descent as follows 
bryo rodent differs from the adult Monotreme in having the 
betana ‘t inguinal cone.’ 
The descent is not found in the Monotremes and lower vertebrates, 
and must have arisen in higher mammals. 
In these the descent is associated with the modification of the belly- 
wall, the ‘‘inguinal cone.’’ In seeking a cause for the production 
of this modification of the belly-wall, some external factor and not 
internal organs is to be considered. 
This external factor in the modification of the muscular body-wall 
was a mammary glan 
The simplest Marini gland is the small area of skin glands 
with well-developed skin muscles in the inguinal region, on each side, 
in the Monotremes. This is present in the male also, but is to be 
considered as secondarily derived from the female. 
That such a body might react upon the body-wall is indicated by 
the existence of the cremaster muscles in the female marsupial, gland 
and muscle functioning together. Some such change in connection 
with a mammary gland may have formed the “‘ inguinal cone.” 
This cone in the male was utilized as being the point of least 
resistance in the body-wall, and evaginated when the testes enlarg 
periodically. Though such a cone is present in female animals, it is 
not associated with the ovary, as this does not enlarge. 
The origin of the inguinal ligament remains unexplained, but this 
also may have been handed over from the female, with other organs 
connected with the mammary gland. 
Granting’ the scrotum represents such a primary mammary gland 
area, we would expect to find no true mammary glands in males., 
Those present anterior to the inguinal region are easily explain ed = 
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