182 General Notes. [February, 
directed towards the roof of the amniotic cavity, the reverse of 
the eutherian embryo. An umbilical stalk is also formed, which 
springs from the dorsal surface of the embryo and passes toa 
partially zonary placenta, disposed in relation to the uterine walls 
in exactly the same way as that seen in the embryo of Carnivora. 
If we now regard the dorsal surface of the embryo of Peripatus 
edwardsti as homologous with the ventral surface of the embryos 
of Carnivora, the resemblance between the modes of development 
of these two types becomes still more startling. While it is 
manifestly absurd to even attempt to suppose, on the strength of 
these resemblances, that there could be any genetic affiliation 
between the Carnivora and Malacopoda, the only way out of the 
difficulty seems to be to suppose that the similar methods of 
development of the two arose in response to the similar conditions 
which environ the ovum during its early stages of growth. 
The differences between Von Kennel and Sedgwick, as to the 
modes of development of P. edwarasti and P. capensis, it seems to 
me, may be readily understood and reconciled when it is consid- 
ered that the first is holoblastic and endocyemate, while in the 
latter the egg is meroblastic, and apparently undergoes an epicy- 
emate process of development. 
All the data in the foregoing paragraphs unequivocally support 
the thesis that the amnion has been developed mainly by mechan- 
ical means and conditions. 
The rigid zona of the epicyemate teleostean embryo, as shown 
in Fig. A, in which the yolk y is a positive quantity, is repre 
sented by the maternal envelope dr in Fig. B, in which the yolk, 
as such, is absent. The gap between the condition of A and that 
of the types with apparently inverted germinal layers, so complete- 
ly elucidated by Selenka, is a wide one; yet it seems easy to pass 
from the primitive condition of A to that of the extremest form, 
viz, the guinea-pig; if the rabbit, mole (Heape), the vole (Kup- 
ffer), and the mouse and rat (Selenka), are considered as inter- 
mediary steps. Socomplete or extreme has been the invagination 
of the embryonic mass or area in these forms that, in the extrem- 
est type, the embryo is finally developed at that side or pole of 
the primitive blastula which is exactly opposite the point where 
the blastodisk was originally formed, as in normal Eutheria. The 
way in which this is accomplished is quite remarkable, and may 
now be described, as the process is a special modification of that 
by means of which the usual endocyemate condition is brought 
about. 
Selenka finds that there is an outer layer of cells, o/, Fig. G, 
split off from the ectoblast, as first described by Rauber, in the 
rabbit’s ovum, and which take no direct partin the formation of the 
embryo. He also finds that upon the further growth of the 
ovum, after the blastula stage is reached and the germinal area Of 
disk is developed, the blastula rapidly elongates in the direc 
