200 DIPS INTO MY AQUARIUM. 



appearances by turns. With the higher power it was easy to see 

 also that there was a rather long, delicate tail or flagellum. 

 Occasionally the creature seemed to rest, when it assumed a more 

 or less globular shape, and the tail could no longer be seen. 



Anyone looking at these remarkable objects for the first time 

 would probably declare them to be animals. Here are eye, tail 

 and locomotion, and certain specks within the body that look like 

 internal organs of digestion and reproduction. What else can 

 they be but animals ? Well, that opens up the question as to 

 what constitutes animality. The old distinctions based on loco- 

 motion, the presence of starch, the method of nutrition, and so 

 on, have broken down under the stress of microscopical and 

 chemical examination, and there seems to be no simple and 

 general principle w^hich can be used as a universal criterion. 

 Some go so far as to say that there is no distinction ; but perhaps 

 it is safer to say that in regard to the lowliest protophyta 2ir\d pro- 

 tozoa the distinction has hitherto eluded discovery. Mr. Gosse 

 decides that EuglencB are animals, and he is no mean authority. 

 But others affirm that they evolve oxygen like plants, while it is 

 clear that they possess the colouring matter of vegetables. Mr. 

 Slack suggests that some of them are plants and others animals, a 

 conclusion w^hich one cannot help feeling is both impotent and 

 useless. 



To the popular mind no distinction is easier to make than the 

 one between animals and plants, but the popular mind is con- 

 cerned mainly with the higher members of these two kingdoms. 

 Science, however, penetrates into an invisible universe, and takes 

 into its reckoning phenomena which are not patent to the unaided 

 eye. Even in the case of a fixed sponge, it is not easy for the 

 tyro to grasp the fact, when told for the first time that he is 

 looking at a colony of animals of a much higher development 

 than many creatures which have mouths, heads, tails, and a 

 digestive apparatus, and that swim about with perfect freedom. 

 And yet there are myriads of animals of lowlier organisation than 

 the sponge, while there are also crowds of minute vegetable 

 organisms which, to the untrained observer, seem much more like 

 animals than does a sponge. Anyone who watches a cluster of 

 monads for the first time under high powers would probably have 



