DIPS INTO MY AQUARIUM. 201 



no difficulty in classifying them, but not so with the man who 

 understands the nature of the problems involved in the question. 

 Let the zoospore of an undoubted plant be placed under the 

 microscope with a monad, and then some indication would be 

 afforded of the difficulty of deciding whether a monad was a 

 plant or an animal. The subtlest analyses of the chemist must be 

 called into requisition in many instances, but even then there 

 would be left some doubtful organisms in which no universal 

 characteristic of either plant or animal could be detected. Sub- 

 stances which, like chlorophyll, the green colouring matter of 

 plants, were long thought to be characteristic of vegetable 

 products, are found to occur in animalcules. Cellulose, of which 

 the walls of plant-cells are built up, is now known to enter into 

 the composition of the outer layer of sea-squirts, while in some 

 vegetables there is actually the digestion of starchy and nitro- 

 genous matters in imitation of animal nutrition. Most animals, it 

 is true, live on organic materials ; but so do the Sundew and 

 Venus' Fly-trap, to say nothing of more secret digestive processes 

 like that carried on in the seed of the vetch. The fungus of the 

 tan-pit {^thaliiim) not only moves about in its earlier stages of 

 development, but even feeds on solids. Then the familiar pheno- 

 menon of respiration is not the ''fixed quantity" it used to be 

 thought, for, as is now well known, plants which give out oxygen 

 during daylight evolve oxygen in the dark — that is, the vegetable 

 kingdom becomes animal during the night. Moreover, the vast 

 group of fungi do not utilise carbonic acid ; but, like typical 

 animals, inhale oxygen both by day and night. There is, then, a 

 scientific No-niafi s-land, wherein dwell things innumerable, which, 

 according to every canon that has yet been tried, cannot be finally 

 arbitrated upon, and which may be called either animal or 

 vegetable. 



Of these I prefer to regard Eiiglence. as forming part, and the 

 differences among naturalists on the point warrant no other con- 

 clusion. Prof Nicholson decribes them under the heading of 

 Infusoria^ and states that they have an oral opening for the incep- 

 tion of food. He also thinks the red spot may be some kind of 

 sense-organ. But he admits that they occupy a doubtful position. 



The reproductive process of Eugleticc does not enable us to 



Journal of Microscopy and Natural Science. 



New Series. Vol. III. 1890. p 



