62 



Aquatic ILxtt 



(Opercularia), when introduced on 

 water plants will live indefinitely in 

 aquaria, appearing as many thread-like 

 masses covering the vegetation. Their 

 points of interest, however, are best dis- 

 covered with a microscope. 



Hydra, the water polyp, a tube-like 

 animal with tentacles, in structure allied 

 to the sea anemones, when it has been 

 introduced will grow widely over the 



Marsilia or Water Clover 



entire aquarium for a great length of 

 time, and when it does disappear may 

 be looked for later. Its movements dur- 

 ing the capture and digestion of small 

 animalcules are interesting. Mature 

 goldfish seldom harm them, due to their 

 stinging properties, and to the fact that 

 they may contract into small jelly-like 

 masses, difficult to remove from the 

 walls of the aquarium. In a tank con- 

 taining fry of goldfish they are as a 

 scourge, killing all that come in contact 

 with the tentacles. Both the freshwater 

 sponge and Hydra grow well on Blodea. 

 For those who teach zoology a hydra 

 aquarium is of great value. 



An excellent natural food for fishes 



is found in the small Crustacea which 

 rapidly appear in stagnating water, or 

 water to which decaying plant remains 

 are added, and then covered. They may 

 thus be grown as desired, and later given 

 to the fishes. Most of the fresh water 

 snails, Physa and Lymnaea, and particu- 

 larly the latter, while doing well in the 

 aquarium, will, if their numbers are un- 

 checked, consume the vegetation. 



Forms of animal life which have not 

 received much attention, and which are 

 well worth a trial in aquaria are the 

 freshwater mussels, which are found in 

 a great many gravel-bottomed, unpol- 

 luted streams. Among the species best 

 adapted to aquarium life are the Big 

 Blue Point (Amblema rariplicata) , 

 Monkey Face (Quadrula) , and Heel- 

 splitter (Lastcna suborbiculata). They 

 will survive only when the size of the 

 aquarium is such that extensive oration 

 takes place. Their movements will in- 

 terest all — the protrusion of the curious 

 foot from the shell for locomation, and 

 of the tube-like syphon for the purpose 

 of drawing in the food and air-bearing 

 water. 



An animal holding its own in aquaria, 

 and of interest on account of its out- 

 side gills while in the immature stage, is 

 the salamander (Amblystoma) , secured 

 along brooks and in ponds. It is, how- 

 ever, apt to depopulate the aquarium of 

 its smaller inhabitants. 



The extremely thin surface layer of 

 water in contact with the air acquires 

 physical properties comparable to those 

 of a fine membrane. This is demon- 

 strated when a quantity of Daphne is 

 placed in an aquarium. Unless the water 

 is agitated some will be entangled in the 

 film, and, unable to descend, will perish. 

 If one from below should swim too close 

 to the surface, it too will become entan- 

 gled, float above water, and meet a like 

 fate. It is this film that enables one to 

 float a needle. 



