aquatic %itt 



51 



the reaction of the living cell in response 

 to stimuli, in the contraction of the 

 spiral "muscle" in the thread-like stalk 

 or pedicle by which the animal is fasten- 

 ed to plants, etc. Amoeba are frequent 

 inhabitants of the surface of the mud 

 covering the bottom, and through a study 

 of them the fundamental facts of life 

 will be better understood. These min- 

 ute forms are not difficult to remove 

 from an aquarium for examination with 

 a long pipette, without otherwise disturb- 

 ing the whole. It is not so easy, how- 

 ever, to catch the larger rotifers or 

 wheel animalcules, or the small crusta- 

 ceans, which requires the aid of a small 

 net of silk gauze. 



It will certainly excite interest to 

 watch under the microscope living ro- 

 tifers (say Branchionus) or cladocerans 

 {Daphnia, etc.). They afford views of 

 the living workings of the inner organs, 

 as the stomach, brain, heart, and even 

 of a living embryo in the process of seg- 

 mentation, and so on. Not less enter- 

 taining and educational is the observa- 

 tion of a Hydra catching infusoria and 

 other foods, or of mosquito larvae, which 

 are also wonderfully transparent. 



The observation of the higher plant 

 life also offers a source of no less enjoy- 

 ment, as aquatic plants afford particu- 

 larly fine opportunities in many ways to 

 examine, without further preparation, 

 the inner structure of the plant and plant 

 cell, besides for instance the methods of 

 plants for protection against attacks by 

 snails, and many other interesting adap- 

 tions of submerged plants. Let us take 

 as an example the formation of air- 

 cells, enabling plants to float, for the 

 study of which the different kinds of 

 Lemna and the leaf-stalks of Myriophyl- 

 lum are very fine objects. The structure 

 of the leaf may also be seen without 

 preparation in Fontinalis and Anacharis. 



while one of the most interesting phe- 

 nomena, the flow or circulation of pro- 

 toplasm within the cell, can easily be ob- 

 served in Char a, Nitella, Vallisneria, 

 etc. All root ends of plants are provided 

 with a sort of protective cap (calyptra), 

 which is nowhere more plainly to be seen 

 than on the rootlets of Lemna. And by 

 the way, those not informed often er- 

 roneously regard the roots of Lemna as 

 stalks of the floating leaf, which is really 

 not a leaf. As a matter of fact Lemna 

 have no leaves, but the apparent floating 

 leaf is a stalk contracted into leaf-shape, 

 from which, as in other plants, the 

 roots descend. 



These few examples prove to what 

 degree the use of a microscope may en- 

 rich the knowledge of an aquarist, and 

 the better enable him to rationally care 

 for his pets, the fishes and plants. But 

 this is not the main profit derived. It 

 is the deepening of his knowledge of the 

 complicated interdependence of life and 

 its hidden laws, as between animal and 

 plant aquatic life. Only he who is also 

 acquainted with the microscopic aquatic 

 life will be able to fully understand the 

 law of "biocenosis," the relation of or- 

 ganisms to other organisms with which 

 they live. It must have been actually 

 seen how each is interwoven with the 

 other, how the bacteria in the sediment 

 and sand, the rhizopods and the algae 

 contribute to the aeration and are, there- 

 fore, necessary for the well-being of the 

 whole aquarium. From the manner which 

 the aquarium is inhabited by these beings 

 invisible to the naked eye, the aquarist is 

 enabled to arrive at conclusions as to the 

 dangers threatening or as to the safety 

 and stability of his little world or com- 

 munity. The occurrence of sulphur-bac- 

 teria, principally Beggiatoa, indicates 

 imperfect aeration as these forms can 

 onlv exist in the presence of sulphuret- 



