334 Mr. Macgillivray's Account of the Outer Hebrides. 



residing in any of these islands, needs not lack employment. At 

 all seasons of the year, objects on which to exercise his craft pre- 

 sent themselves in abundance. The red deer, the swan, the goose, 

 the brent, several species of ducks, mergansers, and divers, the 

 plover, the pigeon, the snipe, and some others, oifer abundant oc- 

 cupation. To these may be added the seal, the otter, and the nu- 

 merous marine and fresh water fishes, which will be noticed in a 

 subsequent section. The various economical purposes to which 

 these animals are or might be applied, will also be treated of in a 

 separate department. 



ART. IV. On the Mechanism of Respiration in certain Aquatic 

 Animals. By William Sharpey, M.D.* 



In the course of some investigations on the development of the 

 tadpole in which I was lately engaged, I was accidentally led to 

 observe, that the surface of that animal possessed the power of ex- 

 citing currents in the water contiguous to it, in a constant and de- 

 terminate direction. This fact, while it was a curious circumstance 

 in the history of the animal in question, appearing to me at the 

 same time of considerable importance in a general point of view, I 

 was induced to inquire how far appearances of the same kind ex- 

 isted in the rest of the animal kingdom. I was aware that many 

 infusory animalcules and zoophytes had been observed to produce 

 currents in the water exterior to their surface, and that in the 

 sponge, as was first satisfactorily shown by Dr. Grant, the water 

 is carried in a uniform direction through certain canals in its inte- 

 rior ; but in prosecuting the subject I have ascertained that pheno- 

 mena more or less analogous are exhibited by extensive tribes of 

 animals of a more perfect structure, in which, to the best of my 

 knowledge, nothing similar has hitherto been observed. Although 

 still occupied with the investigation, yet, as the facts I have alrea- 

 dy made out are, so far as I know, in a great measure new, and 

 appear to me to lead to conclusions of importance, I think it right 

 in the meantime to give some preliminary account of them ; in- 

 tending to resume the subject at greater length on a future occa- 

 sion. 



The larva of the frog, for some time after its exclusion from the 

 egg, has certain small appendages on each side of the head, to 

 which various uses have been assigned by naturalists, but which 



* This paper of our excellent friend Dr. Sharpey has 'already appeared in the 

 pages of the Edin. Med. and Surg. Journal. But as it is perhaps more con- 

 nected with the objects of this Journal, and as, from its importance, it deserves 

 every publicity, we do not hesitate in giving it a place amongst our original ar- 

 ticles. For some remarks and a notice of the previous state of our knowledge on 

 the subject, vide " Nat. Hist. Collections," ir^fra..^^x>. 



