1848.] 



of Terrestrial Planaria. 



163 



composed of old wood and decaying vegetation, in the gardens around 

 Madras. The Natives call them leeches, to which animals they cer- 

 tainly, at first sight, bear a considerable resemblance ; while the 

 long train of silvery slime which they leave behind them in their 

 course, seems to invest them with an analogy to the snail. But 

 the extreme simplicity of structure apparent on a closer examination 

 shows that they cannot be included either with the molluscous or ar- 

 ticulated animals. They belong, in fact, to a species of the exten- 

 sive and ill-defined genus — Planaria. 



The body is long, soft, somewhat depressed and unctuous looking, 

 and ends anteriorly in a flattened semicircular disc. This, which at 

 first sight might be considered the head, is wholly unprovided with 

 the usual organs. There is no trace of eyes, mouth, or tentacula; 

 but instead of the latter the exterior edge of the disc seems to be in- 

 vested with extreme delicacy of touch, exhibited in its great mobility 

 and its power of contraction and dilation when brought into contact 

 with opposing objects. Viewed from above, whilst the animal is in 

 motion it presents a constantly undulating edge, but the under sur- 

 face seems to be composed of numerous fine papillae, which are sedu- 

 lously applied to every substance encountered in its course, and are 

 protruded and withdrawn, according as any portion of the edge of the 

 disc meets with a foreign body, thereby giving it a somewhat crenel- 

 lated appearance. The only other organ observable, is a slit or 

 opening in the middle of the lower surface, somewhat more than half' 

 way from the anterior extremity, whence a white membranaceous cup 

 or syphon is exserted, serving the animal with the means of extract- 

 ing the nourishment, drawn from decaying vegetation, on which it 

 subsists. It may with truth be said to carry its mouth in its sto- 

 mach. But this provision has only been seen after death. During 

 life the orifice itself is not apparent, even with the aid of an ordinary 

 lens, and I have never seen the cup or sucker in use. 



Its motion in crawling is somewhat undulating, and appears to be 

 effected by means of a strong muscle extending the whole length 

 of the under surface or foot, the anterior extremity being generally 

 raised and employed as a feeler. When it reaches the end of a 

 leaf or twig it stretches forward in search of a new resting place, 

 trying in all directions with the disc-like head. If nothing offers 

 it stretches forward until nearly the whole body is disengaged, and 

 it is left at length hanging from the posterior extremity, by means 

 of the viscid secretion, which, on other occasions, marks its track, 



