130 A. A. W. HUBRECHT. 
extent now that the number of fossil mammals, about whose 
placentation we will never know anything, is so very much 
more considerable than that of the living representatives of 
the Mammiferi.! Especially the very early stages in the 
formation of the placenta and the mutual relation as well 
as the details of maternal trophospongia and embryonic 
trophoblast should guide us in comparing placentas and in 
deciding about their amount of similarity and homology. 
And we will then certainly not be inclined to adopt Strahl’s 
latest scheme for the arrangement of the different plans 
of structure of the placenta? (06). The amount of blood- 
relationship which comparative anatomy (in its other chapters 
than that concerning placentation) enables us to establish 
between the different families of the mammalian stem obliges 
us to reject his plan of classification. 
1 The attempt lately made by Strahl (06) to introduce a new classi- 
fication, with a corresponding novel terminology for the mammalian placenta, 
is decidedly premature, and as such detrimental to real progress on this head. 
It condemns itself, where Strahl adduces (’06, p. 275) in its favour, “ Dass 
wir nach derselben die bisher bekannten Placentarformen gut gegen einander 
abgrenzen konnen. Wir brauchen keine Uebergangsformen zu notieren . . .” 
and further, ‘‘ Ausserdem schalte ich dabei vorlaufig einige seltenere, mir aus 
eigener Anschauung nicht bekannte Placentarformen aus, wie sie gewisser- 
maassen als Specialitaten in einzelnen Tieren vorkommen.” 
This immature attempt may appear satisfactory to its author—who in a 
later publication (’07, p. 19) has, however, already proposed certain correc- 
tions—but it breaks down (independently of the general considerations just 
brought forward) in the very primary subdivision into Half-placenta (Semi- 
placenta) and Full-placenta (Placenta), when we consider that, according to 
Strahl’s own definition, the mole ought to be removed from the second, 
Perameles from the first subdivision. 
The principles of Strahl’s system are decidedly artificial, and may satisfy the 
anatomist who has to consider the human placenta in the light of comparative 
anatomy. But the zoologist, who considers only the phylogenetic develop- 
ment—so very difficult to construct—as a trustworthy guide to classification, 
will prefer to abide for the present, and to look forward for new data, before 
proposing a new classification for the so diverse phenomena of placentation. 
2 As, for example, where he classes together as Mammalia choriata C. 
semiplacenta diffusa: Cetacea, Suid, Equide, Camelide, Manis, Tapir 
Hippopotamus, Lemures. 
