260 Dr. R. von Lendenfeld on Guard-Polyps 
of the capsules. In the present case this test succeeds very 
easily. When a transverse section through the margin of the 
umbrella under the olfactory pit is brought under the covering- 
glass in such a manner that the olfactory pit shows freely, 
and then its sense-epithelium is touched with acetic acid, the 
urticating capsules go off one after the other, those first which 
lie nearest to the irritated spot. 
If it is thus rendered probable that the granular threads 
with which the cnidoblasts are certainly, and the irritated 
sense-epithelium perhaps, in continuity, this mode of discharge 
of the urticating capsules leads us to consider how the capsule 
is burst. We have here no mechanically acting cnidocil ; and 
therefore cannot regard a pressure exerted from the sides upon 
the cnidoblast as the cause of the rupture. It seems to me 
rather to follow necessarily from the state of matters described 
that the irritation is transferred through the fibre to the plasma 
of the enidoblast, and causes this to contract; for it is pro- 
bably a fundamental property of still undifferentiated plasma 
to contract upon irritation. The plasma of the cnidoblast, 
however, has the form of a closed tube; and the uniform con- 
traction of such a tube will have as its consequence a pre- 
ponderance of the pressure on the sides of the elongated 
capsule, by which the nettling thread will then be pressed 
forth. 
These urticating capsules cccur exclusively in that part of 
the disk which, as the so-called covering lamina, closes from 
above the cavity in which the marginal corpuscle lies. At 
any rate they serve as defensive weapons for the protection of 
the marginal corpuscles, and are consequently analogous to that 
urticating pad which runs above the nervous ring of the 
Craspedota. 
Ill. On Urticaiing Cells. 
The valuable investigations of Hamann * have essentially 
advanced our knowledge of these peculiar microscopic 
weapons. Wright t, the discoverer of the palpocils of Syn- 
coryne, Without further consideration ascribed to the enidocils 
the function of tactile sete; but Schultze ft raised doubts as 
to this interpretation, and Hamann now seeks to prove that 
in the urticating cells we have not to do with sense-cells. I 
believe that all zoologists will probably adopt this opinion. 
Hamann endeavours to prove that the centripetal process 
* Jenaische Zeitschrift, Bd. xv., “ Ueber Nesselkapselzellen.” 
+ Proc. Roy. Phys. Soc. Edinb. vol. i. p, 541. 
¢ ‘Cordylophora,’ p. 22. 
