276
FINDLAY E. RUSSELL
from 4 to 226 p in length. The intracapsular space contains a clear
fluid which according to some investigators contains the venom.
The cnidoblmts are produced within interstitial cells distant to their
final site in the epithelium. None originate in the tentacles. They
migrate to their h a 1 location in the ectoderm by ameboid activity and
passive transport. The cnidoblast adjusts itself to a superficial position,
with that part of the cell containing the nematocyst directed so that
the thread can be discharged into the offending or stimulating organism.
The cnidocils, when present, are receptor structures which receive and
conduct stimuli to the cell. However, stimuli may be received and
conducted by the cell membrane independent of cnidocils.
Under normal conditions, nematocysts discharge in a highly
localized fashion in response to a specific localized stimulus (Pantin,
1942). There does not usually appear to be any coordinated response by
the various parts of the animal. Although discharge may be elicited
by direct mechanical stimulation, a sensitizing chemical stimulus will
greatly reduce the threshold at which the discharge takes place. The
cell appears, for example, to be particularly sensitive to lipoidal
substances absorbed upon proteins. Nematocyst sensitization by various natural occurring and synthetic surface-active substances has
been studied extensively by Yanagita (1960).
The mechanism for the discharge of nematocysts is an interesting,
though controversial one (this problem is reviewed by Chapman and
Tilney, 1958; see in particular Picken, 1963; Robson, 1963; and
Picken and Skaer, 1965). I n some instances it would appear to involve
an increase in the permeability of the capsule wall following appropriate
stimulation, with the result that either as a direct response to increased
hydrostatic pressure, or a change in pH, or swelling of the colloidal
substances within the capsule, the tube is forced out as the entire
nematocyst " explodes ". The discharged nematocyst, which may
appear pear-shaped (Fig. 2), consists of a bulb (the old capsule), and
the tube or thread, commonly armed with spines about the base.
The mechanism for transfer of the venom to the envenomized prey or
victim is not thoroughly understood.
Nematocysts have been classified on the basis of structure, function
and taxonomy, but until Weill proposed his elaborate nomenclature
for these structures there was little common communication on their
forms. Weill described seventeen categories of nematocysts and these
have been adopted by many workers in the field.
The classification shown on the opposite page, based upon structure,
is adopted from the discussion by Hand (1961).
From the functional standpoint, nematocysts have been divided
FINDLAY E. RUSSELL
from 4 to 226 p in length. The intracapsular space contains a clear
fluid which according to some investigators contains the venom.
The cnidoblmts are produced within interstitial cells distant to their
final site in the epithelium. None originate in the tentacles. They
migrate to their h a 1 location in the ectoderm by ameboid activity and
passive transport. The cnidoblast adjusts itself to a superficial position,
with that part of the cell containing the nematocyst directed so that
the thread can be discharged into the offending or stimulating organism.
The cnidocils, when present, are receptor structures which receive and
conduct stimuli to the cell. However, stimuli may be received and
conducted by the cell membrane independent of cnidocils.
Under normal conditions, nematocysts discharge in a highly
localized fashion in response to a specific localized stimulus (Pantin,
1942). There does not usually appear to be any coordinated response by
the various parts of the animal. Although discharge may be elicited
by direct mechanical stimulation, a sensitizing chemical stimulus will
greatly reduce the threshold at which the discharge takes place. The
cell appears, for example, to be particularly sensitive to lipoidal
substances absorbed upon proteins. Nematocyst sensitization by various natural occurring and synthetic surface-active substances has
been studied extensively by Yanagita (1960).
The mechanism for the discharge of nematocysts is an interesting,
though controversial one (this problem is reviewed by Chapman and
Tilney, 1958; see in particular Picken, 1963; Robson, 1963; and
Picken and Skaer, 1965). I n some instances it would appear to involve
an increase in the permeability of the capsule wall following appropriate
stimulation, with the result that either as a direct response to increased
hydrostatic pressure, or a change in pH, or swelling of the colloidal
substances within the capsule, the tube is forced out as the entire
nematocyst " explodes ". The discharged nematocyst, which may
appear pear-shaped (Fig. 2), consists of a bulb (the old capsule), and
the tube or thread, commonly armed with spines about the base.
The mechanism for transfer of the venom to the envenomized prey or
victim is not thoroughly understood.
Nematocysts have been classified on the basis of structure, function
and taxonomy, but until Weill proposed his elaborate nomenclature
for these structures there was little common communication on their
forms. Weill described seventeen categories of nematocysts and these
have been adopted by many workers in the field.
The classification shown on the opposite page, based upon structure,
is adopted from the discussion by Hand (1961).
From the functional standpoint, nematocysts have been divided