FOUND IN THE NORTHUMBERLAND LAKES. 413 
it is difficult to conceive how they can be withdrawn; and, there- 
fore, it is probable that the tentacles can only be disengaged by 
moulting these organs, which seem to be very slightly attached 
by the neck of the flask-like portion. 
This, however, may not be the only reason why these weapons 
are left in the wound. It has been stated that they are stinging 
as well as captor organs, and if so, may require time to pour the 
poison into the wounded animal, The deadly fluid is probably 
contained in the bulbous portion of the instrument, and by the 
contraction of its walls may be forced through the other extre- 
mity which is perforated ; at least from the extreme point, a long, 
delicate filament, fig. 10 d, almost invariably protrudes, resem- 
bling very closely the appearance of the long process attached 
to the stinging bodies thrown out of the papille of olis, and 
from the tentacles of Actinia. But other bodies much more 
closely resembling the stinging organs of these animals, were 
found strewed about, associated with the captor organs. These 
bodies, fig. 11, are minute elliptical sacs, with a long, slender 
filament from one end, like that just mentioned, from the pointed 
extremity of the captor organ. The filaments of both these 
bodies have a double margin, and are apparently tubular. Now 
it is more than probable that these elliptical sacs are thrown out 
of the captor organ, and that the filament, so frequently seen 
issuing from its pointed extremity, belongs to one of them about 
to be exserted. 
We thus see that Hydra is provided with a most efficient 
stinging apparatus, which having penetrated the surface of its 
prey, remains fixed there, discharging into the wound its poison- 
bearing filaments. No wonder then that the embrace of these 
animals should be so deadly to the animalcule that comes within 
their reach ; and that the worm, so tenacious of life, should fall 
paralysed from their touch, and die, as we are told, almost without . 
a struggle. 
The captor organs of Hydra viridis are exactly similar to thase 
just described, but are scarcely more than half their size. In this 
species, too, they are cast from the tentacle. 
Corda considers the arrow head, and what he calls the ovate 
