588 Causes of Volcaiiic Aclion, 



back, just above the sucker. The dorsal vessel begins in a 

 sort of swelling above the mouth ; and, after it has passed 

 beyond the middle of the body, it becomes sensibly attenuated. 

 It is not fibrous, and, indeed, exhibits no marked structure 

 beyond a very fine and faint reticulation of the surface when 

 exposed under a high magnifier. The space between the 

 intestine and margins of the body is compactly filled with 

 myriads of oviform bodies, which seem to lie, without any 

 particular order, in a gelatinous fluid : they are roundish, 

 opaque, and encircled with a rim or pellicle of transparent 



jelly. 



I have twice found this leech in specimens of Cyprina 

 islandica dredged up in Berwick Bay. They were lurking 

 between the cloak and branchiae, and doubtless had sought 

 out the site for a less harmless purpose than shelter from foes ; 

 but, so far as I could judge from external appearances, the 

 oyster had not suffered any material injury. 



On the suggestion of Lamarck, it has been here considered 

 a species of Phylline ; but it will not correspond with the 

 character of the genus, for the large terminal disk or sucker 

 is not armed with hooks, as Lamarck's definition expresses, 

 but is quite smooth. Nor has the skin the slightest appear- 

 ance of circular rings, or rugae, even when contracted and 

 hardened by spirits ; and its whole anatomy is so unlike that 

 of Annelides, and more especially of the true leeches, that it 

 strengthens an opinion of Lamarck's, of there being a class of 

 animals, yet unestablished, between the Annelides and the 

 worms. 



Art. IX. On the Cause of Volcanic Action ; a Reply to Professor 

 Higginss Revietv, in p. 434, 4-35., of Dr. Daubenys Theory. 

 By Dr. Daubeny, King's Professor of Botany and Chemistry in 

 the University of Oxford. 



Sir, 

 If your correspondent, Mr. Higgins, will consult the forth- 

 coming Part of the EncyclopcEdia Metropolitana (namely. 

 Part xxxix.) when it appears, I flatter myself he will find, in 

 the course of the article on Geology, which it is to contain, 

 an answer to most of the objections brought forward, as 

 applicable to that theory, by which I have attempted to ex- 

 plain the phenomena alluded to. He will at least see discussed 

 at considerable length the question, whether the bases of the 

 ordinary constituents of lava are likely to be so acted upon 

 by water, as to produce the requisite degree of heat in con- 

 sequence of its presence. 



