54 Bibliographical Notices. 



ing these with a hand-lens as they floated in the water, I was 

 struck with the appearance of a Mucedo-Wke. 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 Tiigher 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 cariying 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 peduncle 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 Conybearei, of the natural size, growing upon an 

 empty Buccinum-sheW. 



Fig. 2. A portion of a colony, magnified : a, a, gonoblastidia loaded with 

 gonophores and extended ; h, gonoljlastidium 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 If. 

 By John Gwyn Jeffreys, 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 



