202 Law of. Flectro-Magnetic Induction. 
spring, when it is warmed anew to life, and the deniere once 
more appear. 
- 25. In conclusion, the Hydroidea are animals cetih no external 
organs but tentacles and a mouth, and no internal, but.a simple 
stomach cavity and its prolongation below in the form of a tube or 
 tubularaxis. Without any special glandular system, and with but 
a single opening to the alimentary cavity,—the food is digested by 
the gastric fluid of the stomach, and the refuse matter ejected. by 
the mouth. Without a special absorbent or a circulating system 
or branchie,—the digested material of the stomach passes down- 
ward into the tubular axis, where it has a vibratory or cyclosis 
movement ; and here it is farther elaborated by the action. of air 
from the admitted water, and becomes absorbed and assimilated 
by the surface of the cavity, or of the tubular organs, cavities, 
or pores, connected with it—these chyloid fluids acting in place 
of a proper circulating fluid; aération: of:the same ‘also takes 
place through the tentacles and the exteriorsurface of the animal, 
which receive air from the waters about them. Without ovarian ‘ 
glands, almost any part of the polyp. possesses the reproductive 
function, excepting the tentacles; and buds or ovules are formed, 
and pass out'directly from the dite of the animal. Without a 
distinct 
nervous system, in addition to the above negative char-. 
ery. part seems equally a centre of organic forces (unless _ 
acters, evi 
we except the tentacles), and consequently sections made almost 
re still live and puree eat’ the entire polyp — 
mos 
poet XVIl. Bi oo of Bioctem Macnee iididiens ont Cuas. G: 
Pace, M. D., Prof. Chem. and Pharm., Columbian. College, 
- Washington, DA: 
ay the first fruits of the Arial Galvanometer, (see this Jour., i, 
‘ii Ser., 242,) I have to communicate the establishment of a defi- 
nite law of inductive action of currents upon soft iron, and a direct 
-~iprai tical corroboration of the law of Ampere as to the modifying 
influence of distance upon induction, 
ci 
rded ne. action b of a ae spirals, or concentrated 
: iid ie eer re soe 
First: As regards the inductive action with reference t to sur-- 
and mass. mass.—Although. the weight of authority upon. this 
