PARTS OF ANIMALS, IV. v. 



all respects like a plant : it lives only while it is 

 growing on to something, and when it is pulled off it 

 dies. What are called Holothuria and the Sea-lungs" 

 and other similar sea-animals differ only slightly 

 from the sponges in being unattached. They have 

 no power of sensation, but they live just as if they 

 were plants unattached to the soil. Even among 

 land-plants such instances exist : hving and groΛving 

 either on other plants or quite unattached : for 

 example, the plant found on Parnassus, sometimes 

 called the Epipetron (Rockplant). If you hang this 

 up on the pegs^ it Λvill keep alive for a consider- 

 able time. Sometimes it is doubtful Avhether these 

 Ascidians and any other such group of creatures 

 ought to be classed as plants or as animals : In so far 

 as they live only by growing on to some other object 

 they approach the status of a plant ; but yet they 

 have some fleshy substance and therefore probably 

 are capable of sensation of a kind. 



This particular creature (the Ascidian) has two 

 orifices and one septum ; by one orifice it takes in fluid 

 matter for food, by the other it discharges the surplus 

 moisture ; so far as can be seen it has no residue like 

 the other Testacea. And as no plant ever has any 

 residue this is a strong justification for classing it 

 (and any other such animal) as a plant. Through its 

 middle there runs a thin partition, and it is reason- 

 able to suppose that the governing and vital part of 

 the creature is situated here. As for what are called 

 Knides or Acalephae,'' they are not Testacea, it is 

 true, but fall outside the defined groups. In their 

 nature they inchne t0Λvards the plants on one side 



Those common to the Mediterranean are more virulent in 

 their stinging powers than those of the north. 



335 



