78 A. A. W. HUBREOCHT. 
according to which I should desire to conduct both the collect- 
ing and the working out of the subject-matter of these investi- 
gations. I resolved to extend certain researches with which I 
had been occupied for the last few years, and which had refer- 
ence to the earliest developmental stages and the formation of 
the germinal layers of mammals, as well as to the numerous 
and often unexpected points of difference which we observe in 
the first origin and in the detailed anatomy of the placenta 
(afterbirth) of different mammals. 
Of late years the mammalian placenta has been more closely 
studied by numerous anatomists, but nevertheless its highest 
stage of differentiation as found in the human subject is yet so 
imperfectly understood (genetically) that a comparative investi- 
gation of the more primitive orders of mammals is an imperious 
necessity. As in all other attempts at comparative analysis, 
so in this case the selection of the material that is to furnish 
the bases of comparison is most important. 
Now the lowest mammals (Ornithodelphia, Didelphia) are as 
yet deprived of a placenta; this organ has only become developed 
in later, more highly differentiated orders. It is thus the very 
youngest organ which we meet with in mammals, the latest 
acquisition by the gradual perfecting of which they have 
obtained a considerable advantage over the lower Vertebrates. 
' The order of the Insectivora is regarded as being the most 
archaic among the Mammalia Placentalia, both on account of 
paleontological and of anatomical data. And so the objects of 
comparison had to be chosen in the first place among these 
more primitive forms. 
Several years ago I commenced to study the process of 
placentation in three European representatives of the order 
Insectivora—the hedgehog, the mole, and the shrew,—and have 
published part of the results of these investigations. 
In the Indian Archipelago other genera of the same order 
occur which are entirely absent in Europe. Towards these my 
attention had in the first place to be directed during my stay 
in the Archipelago. They are the genera Tupaja and 
Gymnura, of which the latter very soon proved too rare to be 
