V Minute Inhabitants of Aquaria £.. 



■I? 1 : PERRY BRUCE CLARK f> 



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One of the most interesting phases of 

 the aquarium and its maintenance, to my 

 mind, is that which embraces the obser- 

 vation and study of its minute inhabi- 

 tants. Any one who possesses an aquar- 

 ium, an old one used for the propagation 

 of plants is best, or a small amount of 

 stagnant water, will have sufficient ma- 

 terial to pursue this study. A good hand 

 lens will suffice for the larger animals, 

 such as the crustaceans, but a low-power 

 microscope is necessary for the observa- 

 tion of the smaller forms. I would sug- 

 gest that any aquarium society interested 

 in this subject purchase a microscope, 

 and then lend it out to the different mem- 

 bers, as I have no doubt that almost all 

 fish and aquarium fanciers will find the 

 observation of these tiny animals a very 

 fascinating pastime. 



To approach this subject properly we 

 must begin with the most simple forms 

 of life, and gradually work up to the 

 higher forms. The simple form of life is 

 the single cell. This is a small mass of 

 living matter which is able to multiply 

 and form new cells of the same kind. 

 The main bulk of a cell is made up of a 

 viscid, liquid substance called protoplasm, 

 this is very complex, and is composed 

 chiefly of water, in which is dissolved 

 different salts, and in which is also sus- 

 pended fine particles of organic matter, 

 such as is taken in for food, waste prod- 

 ucts of digestion, and other substances 

 which take part in the life activity of the 

 cell. The skin of the cell or cell mem- 

 brane is formed by a hardening of the 

 protoplasm on the outside of the cell. 

 In the protoplasm is suspended a small 

 body called the nucleus, which contains 



the sexual elements, and is the centre of 

 life of the cell. When a cell has reached 

 the maximum of its development a 

 changes begins in the nucleus, the minute 

 chromatin threads or sexual elements 

 (each cell contains both male and female 

 chromatin threads) divide in two parts, 



Diagram of a Cell 



A. Centrosome 



B. Contractile vacuole 



C. Cell membrane 



D. Protoplasm 



E. Nuclear membrane 



F. Chromatin threads 



G. Nucleolus 



H. Nuclear plasm 

 K. Types of bacteria 



a half of each male thread then combines 

 with a corresponding half of a female 

 thread and an equal number of these 

 combined threads place themselves at 

 opposite sides of the nucleus. The nu- 

 cleus now divides, a half going to each 

 end of the cell, which then becomes con- 

 stricted in the centre and finallv breaks 



