188 The Siphonophores. [ March, 
The eggs cast into the water are then impregnated by sperm 
from the male bells. Previously to this event the egg is of course 
incapable of development, and it is an interesting fact that the 
male bells of one colony cannot fertilize the eggs from the same. 
I need not remind the reader how widespread this law is in the 
plant world. Twosexes are joined in the same Aga/ma colony, but 
self-fertilization is not possible. The egg cannot be impregnated 
by the male element from the same Aga/ma as that from which it 
arises, but is cast into the water, and there fertilized by the males 
from another Aga/ma. Artificial impregnation of the egg often 
fails because this principle has not been recognized and followed. 
Although there are very many known examples, where an animal 
has the power of casting eggs capable of development before the 
adult form is reached, nowhere do we find this principle in nature 
better illustrated than in Aga/ma. Even before the Aga/ma has 
doffed features called embryonic, from the fact that they are 
limited to the young, and are not present in the adult, the jelly 
fish lays eggs, which, strangely enough develop into other 
Agalmata, and eventually into the true adult form, which their 
parent had not attained to when they were cast. The egg float- 
ing in the water after the escape from the female bell is trans- 
parent, and has a cell contents, but with no differentiation in 
any part except the existence near one pole of a more trans- 
parent space containing a dot. These structures are called the 
germinative vesicle, and the germinative dot respectively... 
The first changes which I have observed in the egg after 
impregnation, or contact with the male element, is the formation 
in the germinative vesicle of a number of radiating lines, which 
give to it an indistinct likeness to a wheel with radial spokes and 
a central hub, which is represented by the contained dot. At the 
same time there separates from this region of the egg two small 
spherical bodies similar to those cells which in the eggs of some 
other animals have been given the name of direction cells. The 
radiated appearance in the germinative vesicle, is what is known 
as segmentation, and is very peculiar in Aga/ma. 
The next important change in the development of the egg after 
the segmentation above described has taken place, is the disap- 
1Of the obscure method of segmentation among Physophoridz much remains yet 
unknown. The account which I have given of the peculiar radial structure in the 
erminative vesicle may be of something else than segmentation. See P. E. Muller, 
Naturhistorisk Tidsskrift, 3 R. 7 B, 1871. 
