TURBELLARIA. 77 



both salt and fresh water, where they swim about rapidly, 

 by an undulating movement of their body, somewhat after 

 the manner of a leech, and creep with great ease upon 

 aquatic plants. They are generally of small size, but 

 exceedingly voracious. Like the Polypes, they appear 

 capable of almost endless increase by division. Sir J. 

 Dalyell, speaking of the Black Planaria (P. nigra) says, 

 " it is privileged to multiply its species, in proportion to 

 the violence offered. It may almost be called immortal 

 under the edge of the knife. Innumerable sections of the 

 body, all become complete and perfect animals. If the 

 head be cut off, a new head replaces it ; if the tail be 

 severed, a new tail is acquired." 



The mouth of the Planarise is a very remarkable struc- 

 ture. Near the middle of the under-surface there are two 

 transverse slits, from the anterior of which a funnel-shaped 

 organ, like a cup, can be protruded. This acts as a.mouth ; 

 it is soft, highly irritable, and when drawn within the 

 body is folded up, like the bud of a plant. This singular 

 mouth opens immediately into the stomach ; it can be 

 protruded at pleasure, and applied to the surface of such 

 larvae or little worms as may come within reach, so as to 

 suck from them the juices that they contain, or if the 

 prey be small, it is immediately swallowed. 



But the most wonderful creatures belonging to this 

 group are 



The Long Sea-wornis (Nemertes),* occasionally to be met with by 

 the sea-side explorer, coiled up under loose stones. The length of 

 this extraordinary production of Nature is positively prodigious; 

 and its whole history has more the appearance of fable than of sober 

 truth. 



" When I took it up at the sea-side," says the Rev. Mr. Davis (Linn. 

 Trans.), "collecting such an immense creature into an oyster-shell, a 

 very large one indeed, I thought it would have been almost impos- 

 sible to unravel it ; but it is astonishing to think how easily it was 

 disentangled, owing to the extraordinary smoothness of its surface. 

 It is impossible to make even a guess at the length of it when alive, 

 on account of its always extending and contracting itself when 

 touched, and that with such ease, as almost to exceed belief; but I 

 may well say that it is capable of extending itself without incon- 

 venience to twenty-five or thirty times the length that it presents at 

 another period. It being impossible while the animal was alive to 

 make any reasonable conjecture as to the length of it, I took it out of 

 the bottle, and examined it when dead, when I found it to be two- 

 and- twenty feet long, exclusive of the proboscis. Now I give it 



, nemertes, no mistake about it. 



