412 MR. HANCOCK ON A SPECIES OF HYDRA, 
action. The saucer-like vesicle is then seen to have disappeared, 
and the outer vesicle, fig. 10 a, is lined throughout with a delicate 
membrane, 6; in fact, the lips or margins of the saucer-like vesicle 
have unrolled themselves, and now form the upper portion of the 
lining membrane, the saucer itself being the lower portion of it. 
And, moreover, the lining membrane is continued through the 
neck of the outer vesicle, and is seen to be prolonged into the 
stalk, c, supporting the arrow-head ; the barbs, c’, of which, three 
in number, are now very much elevated, being almost horizontal ; 
and thus protruded beyond the surface of the tentacle, are ready 
to lay hold of prey in the manner of a grappling-iron. 
The animal would appear, however, to have the power of 
throwing the whole apparatus from the tentacle. Ifa specimen 
be laid ona piece of glass, and examined through the microscope 
a number of these organs, with the barbs fully extended, will be 
seen scattered about like as many minute Florence flasks; the 
bulbous extremity being elegantly rounded. For the purpose of 
ascertaining if the animal really possessed this power, a small 
worm was given toa polype when under the microscope, and 
carefully watched. The animal was exceedingly cautious in using 
its tentacles, not applying them in their whole.extent, as might 
have been expected, but keeping by far the greater portion of 
these organs perfectly free, and unattached to itsprey. Very few 
of the arrow-heads were exserted, and, apparently, never till re- 
quired ; occasionally certain parts of the tentacles were brought 
into contact with the worm, and then, as it was forcibly drawn 
further into the mouth, the protruded barbs might be seen sticking 
in the surface of the struggling victim. At other times, as it 
rolled about in its vain endeavours to escape, the bulbous extre- 
mities of several of these formidable weapons were seen pro- 
truding from the skin, undoubtedly placed there by the pungent 
embrace of this deadly and determined foe; while others lay 
scattered about in every direction, as if just cast from the tenta- 
cles. It is therefore evident that these weapons can be used 
either as grappling instruments for securing food, or, having been 
plunged into some living prey, can be left half-buried in the 
wound. Indeed when the barbs have been once fairly immersed, 
