and Uriicating Cells. 263 
by Hamann, unite with the supporting lamella, and_ that 
therefore only a supporting function is to be ascribed to them, 
but that jiner threads from the multipolar ganglion-cells run 
up on these pedicles and place themselves in connexion with 
the plasma of the cnidoblast. 
If we compare the morphological characters of the urticating 
cells with the observation of living animals in the aquarium, 
we shall be struck especially by one peculiarity of the areni- 
colous Actiniw; although hundreds of capsules discharge 
5 
themselves when a digestible body touches the cnidocils, not 
fo) 
a single one is discharged when sand falls upon them. If a 
freshly torn-off tentacle is placed under the microscope and 
there are many small animals in the water, we can easily ob- 
serve how every contact cf an animal with the surface of the 
tentacle is accompanied by a salvo of nettling threads, while 
not a single one can be coaxed forth if a rapid current 1s pro- 
duced, and sand-grains, fragments of covering-glass, and the 
like are introduced under the cover. 
In the Actinie therefore it seems to be dependent on the 
will of the animal whether the touching of the enidocil shall 
or shall not be followed by a discharge. If this phenomenon 
be considered in connexion with the fact that urticating cap- 
sules are never discharged when the animal retracts its ten- 
tacles, when the pressure in the vicinity of the cnidoblasts is 
heightened by muscular contraction, and the enidocils touch 
other bodies, [ think I am justified in regarding the following 
rocess of discharge of the urticating capsules as the most 
probable :—There exists a continuous connexion between the 
nervous system and the plasma-mantle of the urticating capsule. 
The urticating capsule is ruptured by the pressure which the 
plasma-mantle exerts upon it *. In Cyanea Annaskala there 
is added to this a stellule which breaks through the membrane of 
the distal pole. In Physalia the plasma has already separated 
muscular fibres. The contraction of the plasma-mantle is tn- 
duced by an excitation proceeding either from the cnidocil or 
from the nervous system. Further, however, a preventive ex- 
citement may tssue from the nervous system, which paralyzes 
the cnidocil—excitation which, under ordinary circumstances, 
would burst the capsule. The nervous system can therefore 
take on the function of a “ preventive centre,” while the dis- 
charge by the cnidocil-excitement is to be compared to a “ reflex 
movement.” Llere therefore we already see the commencement 
of that reciprocation of reflex and preventive action to which 
modern psychology ascribes such great importance. 
* In this I find myself in agreement with Chun (/. c.), 
19 
