1848.] 



of Terrestrial Plamria. 



165 



the alimentary orifice placed a little behind the middle of the body, as 

 in the genus. Habits, terrestrial. Food, decaying vegetable matter. 

 Length about 5 inches. 



The colour is a uniformly dark brown, nearly black, except round 

 the disc, which is white bordered at the very edge with pale brown. 

 On examining the head (as it is most convenient to call this extre- 

 mity) under a powerful microscope, to detect, if possible, the exis- 

 tence of organs of sight or touch, the surface of the paler portions 

 around the white was observed to be sprinkled with dark irregular- 

 shaped specks, which, to the naked eye, seemed the minutest points, 

 but when magnified resembled well defined chromatogenous spots, in 

 what appeared to be the cellular gelatinous mass of which the body 

 was composed, the whole surface of which was covered with a moist 

 secretion, apparently afibrding the material of the shining trail which 

 it leaves in its course. 



The genus Planaria originally established by Miiller and after- 

 wards restricted by A. Duges on the aquatic species alone, was by 

 Cuvier at first conjecturaliy, and afterwards on actual inspection, re- 

 ferred to the class of Parenchymatous Entozoa among the radiated 

 animals, although, as he himself has observed,^ P/a?2flr/<2 ^^.ndi Infuso- 

 ria afford almost the only instances among the animals brought un- 

 der this great division, in which no trace of a radiated structure has 

 been detected. 



Their extreme simplicity of conformation, however, forbids the at- 

 tempt to remove them to a higher place in the chain of being, but 

 the great number of species discovered since the publication of the 

 Regne Animal will probably lead to considerable modifications in the 

 arrangement of the group. Some of the aquatic species described 

 by Dr. J. Rawlins Johnson in the Philosophical Transactions! which 

 were entirely aquatic, exhibited marks of a more perfect organisation 

 in the apparent development of eyes and tentacula. They were also 

 carnivorous and exceedingly voracious, preying even on their own 

 race. Darwin also in the terrestrial species described by him notices 

 numerous ocelli or black eye-like spots, variously distributed over the 

 surface both above and below, which he considered to be imperfect or- 

 gans of vision. In PL elongata however, a species from Tres Mon- 

 tes, in Western America, (lat. 46" 30'' S.) the largest he met with, and 

 which approximates most nearly to ours, they were entirely absent. 



♦ Regne Animal iii. p. 219. 



t Phil. Trans. 18:.'2, p. 437, ib. Plate xlix. fig. 24. 



