132 THE AMERICAN NATURALIST. [Vor. XXXV. 
Among the latter there is notably that of Hubrecht (95), 
which recognizes a polyphyletic origin of the Mammalia from 
viviparous Amphibia. 
Whether or not the embryological data on which Hubrecht 
bases his conclusions justify this interpretation is a question 
on which the writer does not feel competent to ‘express an 
opinion. It may be noticed, however, that Hubrecht's results 
are differently interpreted by Assheton (98), and that his 
hypothesis has not been generally accepted. 
Hubrecht cites in support of his hypothesis the results of. 
Gegenbaur (86), Mivart (88), Osborn (93), and Klaatsch (92). 
These may accordingly be examined at the same time in rela- 
tion to the view of Hubrecht and that of Huxley. 
In the first place, Hubrecht regards the recognition by 
Gegenbaur and Mivart of a fundamental difference between 
the mammary glands of monotremes and those of the higher 
mammals as implying an independent origin of the two 
groups. In some respects this is open to a different inter- 
pretation.  Gegenbaur, while emphasizing the sudoriparous 
nature of the mammary glands of monotremes as opposed to 
the sebaceous nature of those of the higher mammals, was fully 
aware of the limitations of this distinction, since he found 
on the mammary areas of monotremes some glands of the 
latter kind. In discussing the bearing of this he says (p. 35): 
* Aus solchen Verhältnissen des Drüsenfeldes kann man die 
Entstehung der Mammardrüsen bei Monotremen und den 
übrigen Sáugern sich vorstellen. Bei den Einen ist die 
eine Drüsenart, bei den Anderen die andere zur. Ausbildung 
. gelangt." In other words, he perceived that from a diffuse 
condition, in which both kinds of glands were present, we 
may derive the monotreme condition by assuming an exclusive 
` development of one set of glands, and the higher mammalian 
condition by an exclusive development of the other. The 
significance of this was later fully appreciated by Klaatsch 
(92), on the discovery by him of both kinds of glands in the 
peculiar mammary pouches of artiodactyl ungulates. On 
! A more moderate position on this subject has recently been taken by 
Jenkinson ('00). 
