242 Mr. Darwin on several Planarise, 



describe them. They all belong to the genus Planaria, as re- 

 stricted by A. Duges in his memoir* on these animals, and to 

 that of Polycelis of Ehrenberg. They may, however, form a 

 section of the genus, being characterized by their more convex 

 and narrow bodies ; their more distinctly denned foot ; their ter- 

 restrial habits ; and frequently by their longitudinal bands of 

 bright colours. From their colours, from their convex bodies, 

 from their manner of crawling and the track of slime which they 

 leave behind, and from their places of habitation, they present a 

 striking analogy with some terrestrial gasteropods, especially with 

 Vaginulus, with which snail I have several times found them 

 associated under stones. I suspect that, differently from their 

 aquatic congeners, they live on vegetable matter, namely on de- 

 cayed wood ; I suspect this, from having found them repeatedly 

 under this substance, and from having kept some specimens in a 

 box for twenty-one days with nothing else for food, where they in- 

 creased considerably in size. The species which live under stones, 

 both on the grassy, undulating land of northern La Plata, and 

 g on the arid, rocky hills of central Chile, generally inhabit small 

 sinuous chambers, like those frequented by earth-worms, in which 

 they lie coiled and knotted up. They are often found in pairs ; 

 and I once discovered a pair attached together by their lower sur- 

 faces, apparently in copulation. None of these species have the 

 quick and vivacious movements of the marine species : they pro- 

 gress by a regular wave-like movement of the foot, like that of a 

 gasteropod, using the anterior extremity, which is raised from 

 the ground, as a feeler. One species which I tried could crawl 

 well through moss ; another being placed on dry paper was almost 

 killed by it. I put several specimens into fresh water, but they 

 appeared wholly unused to it, and would soon have perished : 

 they seem, however, to prefer damp situations, and the speci- 

 mens of P. Tasmaniana, which I kept in a box with rotten wood, 

 having been neglected to be moistened, all perished, except one 

 large individual which survived quite uninjured, although the 

 wood had become perfectly dry. These animals (especially the P. 

 Tasmaniana) had an immediate apprehension and dislike of light, 

 which they showed by crawling, when the lid of the box was taken 

 off, to the under side of the pieces of rotten wood. My obser- 

 vations, as far as they go, on the structure of these terrestrial 

 species, agree with those given by Duges on the structure of the 

 aquatic species. The figure given by this author of the ramified 

 digestive vessels of P. lactea is quite similar to a drawing that I 

 made of this part in the P. pallida from Valparaiso (which, from 

 being nearly colourless, allowed the best opportunity of observa- 



* Annales des Sciences Naturelles, October 1828. 



