THE VOYAGE OF THE BEAGLE 



37 



always having something to attract his attention; but in 

 these fertile climates, teeming with life, the attractions are 

 so numerous, that he is scarcely able to walk at all. 



The few observations which I was enabled to make were 

 almost exclusively confined to the invertebrate animals. The 

 existence of a division of the genus Planaria, which inhabits 

 the dry land, interested me much. These animals are of so 

 simple a structure, that Cuvier has arranged them with the 

 intestinal worms, though never found within the bodies of 

 other animals. Numerous species inhabit both salt and fresh 

 water; but those to which I allude were found, even in the 

 drier parts of the forest, beneath logs of rotten wood, on 

 which I believe they feed. In general form they resemble 

 little slugs, but are very much narrower in proportion, and 

 several of the species are beautifully coloured with longi- 

 tudinal stripes. Their structure is very simple: near the 

 middle of the under or crawling surface there are two small 

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

 shaped and highly irritable mouth can be protruded. For 

 some time after the rest of the animal was completely dead 

 from the effects of salt water or any other cause, this organ 

 still retained its vitality. 



I found no less than twelve different species of terrestrial 

 Planaria; in different parts of the southern hemisphere. 8 

 Some specimens which I obtained at Van Dieman's Land, 

 I kept alive for nearly two months, feeding them on rotten 

 wood. Having cut one of them transversely into two nearly 

 equal parts, in the course of a fortnight both had the shape 

 of perfect animals. I had, however, so divided the body, 

 that one of the halves contained both the inferior orifices, 

 and the other, in consequence, none. In the course of twenty- 

 five days from the operation, the more perfect half could 

 not have been distinguished from any other specimen. The 

 other had increased much in size ; and towards its posterior 

 end, a clear space was formed in the parenchymatous mass, 

 in which a rudimentary cup-shaped mouth could clearly be 

 distinguished ; on the under surface, however, no correspond- 

 ing slit was yet open. If the increased heat of the weather, 



s I have described and named these species in the Annals of Nat Hist., 

 vol. xiv. p. 241. 



