454 M. Vogt on some Inhabitants of the Freshwater Muscles. 
although still bearing the vitellary sac concealed in the ab- 
domen. 
The fishes’ eggs are, without doubt, introduced by the respi- 
ratory current of the freshwater muscles. But their early exit 
from the egg, at a period when the embryos of other fishes still 
remain in the egg, as well as their whole manner of existence, 
seem to me to prove that the gills of the freshwater muscles are 
the habitual place of incubation of these embryos. - They are all 
concealed there in the same fashion, with the head turned toward 
the free edge of the branchial lobes ; they thus fill the elongated 
cavities between the two plates of a branchial lobe, and it is only 
necessary to cut the external membrane in order to set the em- 
bryos at liberty. It is then curious to follow the movements of 
the oldest. After making some turns in the vessel contaiming 
them, they return toward the gill, and eagerly attempt to pene- 
trate into it. I have often seen them re-enter the respiratory 
canal, and conceal themselves again in a branchial cavity where 
they then kept quiet. 
I have not been able with complete certamty to ascertain to 
what species of fish these little ones belong. The oldest which I 
have met with had not yet any generic character; they all still 
possessed the embryonic fin continuous around the posterior ex- 
tremity of the body, and the ventral ones were altogether want- 
ing. But as I know the eggs of nearly all the genera of fishes 
inhabiting our soft waters, I have reason to believe that these 
eges are of the Cottus Gobia, Linn., a species common in our 
small rivers. 
These embryos are remarkably distinguished from all those 
which I have hitherto observed ; the vitellus is almost opake and 
of a yellow colour, which, under the microscope, appears of a 
deep brown. The vitellary sac has a very elongated form, and 
the young fish is lodged im a very deep depression of this enor- 
mous vitellary sac. The difficulty of observation which results 
from this disposition is further increased by two lateral swellings 
of the yellow mass, swellings which rise where the pectoral fins 
have to come out. The swellings of the vitellus enter indeed 
into the base itself of the pectoral fin in the more advanced em- 
bryos, and thus conceal all the anterior part of the body. To 
examine the heart and the branchial region of the embryo, the 
vitellary sac must be emptied, which soon causes the circulation 
to cease. 
Embryonic researches among the inferior animals are often 
only rendered so difficult by the want of proper materials. I 
shall be happy if I have contributed to remove some of these dif- 
ficulties, and I am sure that analogous researches on sea mol- 
lusks may lead to numerous discoveries of the same kind. 
