DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
269 
they are, one and all, rich in prophetic characters that have come to perfection in 
larger and nobler types. 
I think it will not be denied that, in the ascent of the types, the Chiroptera are 
above the Insectivora, and as it were a sort of special “new leader” from that 
stock, and that the Insectivora are more or less transformed modifications of what is 
characteristic of the Marsupials. 
I suspect that the existing Insectivores just yield the Zoologist one of his groups 
of types classed together because he knows not what else to do with them ; not forming 
a proper, clear, special branch, or “leader ” of the Mammalian life-tree. They form one 
group, under one designation, just as the poor of this Metropolis form a group ; their 
brand is simply lowliness ; they differ, inter se, almost as much as the whole remainder 
above them differ. The higher forms, however, because of their elevation can afford to 
be subdivided again and again, into Order after Order. 
If we could descend and see the transforming and newly-transformed Placentalia of 
the Eocene epoch, then the Morphologist and the Zoologist would find common ground ; 
the Taxonomy of the latter, however, would be as useless as the titles and distinctions 
of modern society to some undeveloped race of savage men. 
The evidently extreme specialization of the existing Monotremes or Prototheria, and 
their manifest close relationship to the Edentates—a strange, lowly group of Eutherians, 
almost extinct in the Old World, and not potent in genera and species in the New— 
makes it necessary for me, in the present stage of my research, to leave them until I 
have mastered both them and the great Marsupial sub-class. Of the latter, however, 
I can speak already ; and as no interpretation of the meaning of the parts seen in a 
Eutherian skull can be made until they are read in the light of the structure of the 
quasi-reptilian skull of a Marsupial, I shall in this summary compare the two types 
together, using the lower and older as a measure of the higher and newer type of 
skull. 
Anatomists are familiar with the characters of the skull in adult Marsupials ; to 
these may be added others that have turned up to me in the study of the 
development of that type. When these are seen in the light of the types outside 
and below the Mammalia, then that which is typical in a high Mammal, as such, can 
be formulated, and the specialization of this great branch of the Vertebrate stock be 
understood. 
I will therefore, here, give a list of the more important and striking cranial 
characters of the Marsupials, promising to bring forward, as early as possible, the 
figures and descriptions of the skull in various stages and in many kinds. 
But before making this comparison of the characters of the skull in the Marsupials 
with what is seen in the Insectivora, I will state that in the latter—a mere “ Order”— 
the diversity is four-fold that to be found in the Marsupials, which are worthy to be 
put, not as a mere Order, but as a “ Sub-Class.” 
