74 Geology of America. 
cavity occupied by a granular matter, which appears to be of 
the same nature with that which fills the umbilical vesicle of 
the Alcyonella. This matter extends to the extremity of the 
tentacula, which clearly proves that these tentacula are hol- 
low throughout their whole extent, and have each a long cul- 
de-sac, communicating with the cavity which exists between 
the skin of the animal and its intestine. This communication 
is also provided, in adults, with a passage for a fluid which 
circulates in this cavity. 
The Nervous System is composed of a double sub-cesopha- 
gial ganglion, which supplies posterior filaments distributed 
along the cesophagus, and anterior ones, which appear to be 
distributed in front and on the sides. 
After thus regarding, then, the complicated organisation of 
the species of polypi which have been oecupying our atten- 
tion, also the general binary disposition of their organs, the 
position of their nervous system ; after considering, also, that 
they have mouths, in many respects analogous to that of the 
mollusea, and that, like them, they produce the envelope 
which protects them ; and when to this we add certain special 
facts which the Cristatella present, as, for example, having a 
foot which is everywhere contractile, and their secreting, like 
the gasteropoda, a copious viscous matter, we shall be led not 
only to associate them with the class of the mollusca, but like- 
wise to introduce along with them all the animals which are 
farther down the scale. Before, however, maintaining this as 
an irrefragably established fact, we shall request another op- 
portunity of explaining some additional results of our re- 
searches. 
American Geology—Erratic Blooks—Glacial Action. 
Tue October number of the American Journal of Science 
contains an address delivered by Professor Hitchcok to a 
meeting of geologists, which gives a general view of the pro- 
gress of the science in the United States. Some of the de- 
tails are not without interest on this side of the Atlantic. 
Geological Surveys.—It appears that in a considerable num- 
