64. Bibliographical Notices. 
ing these with a hand-lens as they floated in the water, I was 
struck with the appearance of a Mucedo-like growth with which 
many of them seemed to be invested. That this, however, was 
something very different from what it appeared to be, soon be- 
came evident; for if the little medusa was touched with the 
point of a needle, the whole of the flocculent mass would in- 
stantly vanish. 
It needed, however, a higher power of the microscope to 
reveal the true nature of the phenomenon, and show that the 
apparently parasitical growth consisted of the enormously elon- 
gated peduncles of the thread-cell-bearing capsules, each of 
which, as it now proved, had the power, while still carrying the 
capsule on its extremity, of extending itself to a length which 
considerably surpassed that of the longer or vertical diameter of 
the umbrella. 
While the medusa continued to float undisturbed through the 
water, the peduncie would remain projected in a straight line 
from the tentacle, becoming at the same time amazingly at- 
tenuated ; but on the least disturbance it would become suddenly 
shortened to less than the one-twentieth part of its length when 
extended, drawing the capsule back with it in its contraction. 
During the extended condition of the peduncles, they were 
seen, with their capsules, to be in a state of constant vibration. 
This was found to be due to a pencil of long, fine vibratile cilia, 
which, by the aid of a high magnifying power, could be detected 
on the summit of every capsule. 
EXPLANATION OF PLATE II. 
Fig. 1. Heterocordyle Conybearet, of the natural size, growmg upon an 
empty Buccinum-shell. 
Fig. 2. A portion of a colony, magnified: a, a, gonoblastidia loaded with 
gonophores and extended; 6, gonoblastidium contracted; c, po- 
lypite with the tentacles partially contracted, showing that, when 
in this state, the tentacles assume a clavate form. 
Fig. 3. A female gonophore still further enlarged. 
BIBLIOGRAPHICAL NOTICES. 
British Conchology, or an Account of the Mollusca which now in- 
habit the British Islands and the surrounding Seas. Volume II. 
By Joun Gwyn Jerrreys, F.R.S., F.G.S. &c. Van Voorst. 
**SincE the publication of the first volume of this work I have made 
two more dredging excursions to the Shetland Isles, a district which 
is by far the most interesting that I know of for the further investi- 
gation of the British Mollusca. In the interval I revisited the south 
of France, and also went to the Hanse Towns, Denmark, Sweden, and 
