THE OFELET. 
167 
they had fallen, closely withdrawn into tlieir shells. Sup- 
posing them dead, they were taken out, when they directly 
began to emerge ; and when returned to the jar with the 
other Momdontas, they were all in less than live minutes 
clustered round its mouth. On placing them again in the 
jar with the Actinia, though kept there for two hours, they 
did not once show themselves out of the shell. Once more 
placing them along with the other shells, they exhibited 
their former signs of life and activity. The experiment 
was repeated several times with a large Littorina, with the 
same result, evincing fear of the Actinia on the part of the 
Mollusks.”* 
I can only say that Trochus umbilicatus, Littorina littorea, 
and Ch iton fasciculatus have no such fear of yin cereiis ; 
for I have just seen these crawl without hesitation by the 
side of a full-grown and vigorous specimen. 
Tliough sensible pain or irritation does not invariably 
follow the contact of the human skin with the tentacles of 
Anthea, yet their strong power of adhesion is never lacking. 
Dissection reveals the cause of both, in the unwonted pro- 
fusion with which these organs are furnished with cnidai. 
In the outer of the two layers of which the tentacle- 
wall is composed reside the cnidce, excessively numerous 
and thickly crowded ; of two kinds, chambered and spiral. 
But it is in the crimson tips that the cnidce exist in the 
most prodigious profusion. They completely fill the field 
of the microscope, when a portion of the wall, flattened by 
the compressorium, is under view, without the least space 
free of them, not even a line or a point ; but overlying each 
other like herrings in a barrel, yet maintaining a general 
uniformity of direction. 
Within the cnidiferous layer, there is another of pig- 
ment cells, visible to the naked eye as a dark brown or 
* Zoophytes, p. 12<'. 
