VII.] ANIMALS AND PLANTS. 177 



Paramcecium, than it is to a monad. But Paramce- 

 cium is so huge a creature compared with those 

 hitherto discussed it reaches -j^j of an inch or more 

 in length that there is no difficulty in making out 

 its organisation in detail ; and in proving that it is 

 not only an animal, but that it is an animal which 

 possesses a somewhat complicated organisation. For 

 example, the surface layer of its body is different in 

 structure from the deeper parts. There are two con- 

 tractile vacuoles, from each of which radiates a system 

 of vessel-like canals ; and not only is there a conical 

 depression continuous with a tube, which serve as 

 mouth and gullet, but the food ingested takes a 

 definite course, and refuse is rejected from a definite 

 region. Nothing is easier than to feed these animals, 

 and to watch the particles of indigo or carmine accu- 

 mulate at the lower end of the gullet. From this 

 they gradually project, surrounded by a ball of water, 

 which at length passes with a jerk, oddly simulating 

 a gulp, into the pulpy central substance of the body, 

 there to circulate up one side and down the other, 

 until its contents are digested and assimilated. Never- 

 theless, this complex animal multiplies by division, as 

 the monad 'does, and, like the monad, undergoes con- 

 jugation. It stands in the same relation to Hetero- 

 mita on the animal side, as Coleochcete does on the 

 plant side. Start from either, and such an insensible 

 series of gradations leads to the monad that it is 

 impossible to say at any stage of the progress here 

 the line between the animal and the plant must be 

 drawn. 



N 



