INTRODUCTION. 
XXXVll 
by the rupture of its •perihola^ before it can effect the 
emission of its ectlwrmim. At least I liave never met with 
an example of the contrary. 
It has long been known, that a very slight contact with 
the tentacles of a polype is sufficient to produce, in any 
minute animal so touched, torpor and speedy death. Since 
the discovery of these cnidae, the fatal power has been 
supposed to be lodged in them. Baker, a century ago, in 
speaking of the Hydra, suggested that “ there must be 
something eminently poisonous in its grasp;” and this 
suspicion received confirmation from the circumstance that 
the Entomostraca, which are enveloped in a shelly covering, 
frequently escape unhurt after having been seized. The 
stinging power possessed by many Medusa, which is suf- 
ficiently intense to be formidable even to man, has been 
reasonably attributed to the same organs, which the micro- 
sco|)e shows to be accumulated by millions in their tissues. 
Though I cannot reduce this presumption to actual 
certainty, I have made some experiments, which leave no 
reasonable doubt on the subject. First — I have proved 
that the ecthoraum Avhen shot, has the power of penetrating, 
and does actually penetrate, the tissues of even the higher 
animals. Several years ago, 1 was examining one of the 
purple acontia of Adamsia palUata : no pressure had been 
used, but a considerable number of cnida had been spon- 
taneously dislodged. It happened, that I had just before 
been looking at the sucker-foot of an Asterina, which 
remained still attached to the glass of the aquatic box, by 
means of its terminal disk. The cilia of the acontium had, 
in their rowing action, brought it into contact with the 
sucker, round which it then continued slowly to revolve. 
The result I presently discerned to be, that a considerable 
number of the cnidee had shot their ecihoraa into the 
flesh of the sucking disk of the Echinoderm, and were seen 
sticking all round its edge, the wires imbedded in its sub- 
stance even up to the very capsules, like so many pins 
stuck around a toilet pin-cushion. 
To test this power of penetration still farther, as well as 
to try whether it is brought into exercise on the contact of 
a foreign body with the living Anemone, I instituted the 
following experiment. With a razor I took shavings of 
the cuticle, from the callous part of my own foot, as from the 
ball of the toe, and from the heel. One of these shavings I 
