IKF.SII-WATKI; AQUARIA. 2.37 



envelopes are very pellucid. The young of the Lymnaea, as also the 

 full-grown Physse, are very interesting to watch as they ascend and 

 descend through the water by means of a mucus thread which they 

 secrete, but which, ordinarily invisible, can be shown to be present by 

 passing a solid body such as a glass rod between the animal and the 

 point of attachment of the thread. The large bivalves, Unio and 

 Anodonta. may be introduced into the aquarium, and they assist in keep- 

 ing the water clear, but they draw into their systems through their 

 fringed syphon tubes diatoms, desmids, rotifers, and other small swim- 

 ming and floating organisms. If they are in a tank they should be watched 

 and removed as soon as death occurs, which may be known by the 

 gaping of the valves of the shell, since such a large mass of decomposing 

 animal matter kills some of the other inhabitants very quickly, besides 

 giving off a by no means agreeable smell. They will, however, under 

 ordinary circumstances, live several years in confinement. 



Polyzoa are generally not difficult to keep in an ordinary aquarium 

 in moderate quantity. The statoblasts or " winter eggs " should be 

 allowed to remain in the water, for though some of them float on the 

 top of the water, or cling to the sides of the tank, giving it a somewhat 

 untidy appearance if they are in considerable numbers, yet the beauty 

 they display when they burst, and the young individuals come forth, 

 amply atones for the former slight unsightliness. The statoblasts 

 may, however, if desired, be removed, and placed in an auxiliary tank 

 to be kept through the winter. Indeed, it is a very good plan to keep 

 specially interesting microscopic beings in separate small glass vessels, 

 as they are the more conveniently got at when required for examina- 

 tion, and can also the better be preserved from their natural enemies.* 



Fish, as has been mentioned, are usually not very desirable tenants, 

 as they will not join the union and become members of a " happy 

 family." The species best suited for confinement are the Eoach and 

 Prussian Carp. These may lie transferred from their native waters 

 direct, but the Perch, Pike, and Minnow, which also do well, should 

 first be placed in a vessel where the water is changed, but at gradual y 

 increasing intervals, and in about a week or ten days they may be 

 placed in their future permanent home. Gold and Silver Fish, as is 

 well known, thrive well in a small tank, so does the common Stickle- 

 back, or Jack Bannel. This latter is one of the most interesting fish 

 we have, as it builds a nest for its young, and in the spring-time the 

 male is very gorgeous in his rainbow hues. The spawn and fry i & fish 

 can be kept, and are well worthy of examination with the microscope, 

 being especiallv instructive as examples of embryonic development 

 of vertebrates. It must be borne in mind that many creatures 

 feed on the fry, their own parents included. Beetles may be placed 



* Mr Pnttshas introduced an admirable form for this and other purposes. It 

 Birmingham. 



