XV. 



NOTES ON A MICROSCOPICAL AQUARIUM. 



By Isaac Eobinsojs^. 



Head at Hertford, 2ith November, 1881. 



A FEW months ago I set up a small aquarium for the purpose of 

 having living specimens for the microscope readily available. As 

 the plan adopted has accomplished the object in view very satis- 

 factorily, and as the various inhabitants discovered in the aquarium 

 by the aid of the microscope have all been collected in the neigh- 

 bourhood of Hertford, a brief description of them may be of interest. 



The aquarium itself consists simply of an inverted bell-glass 

 about ten inches in diameter and about the same in depth, sup- 

 ported upon an ebonized wooden stand, and having a flat glass 

 cover resting upon its upper edge, for the purpose of preventing 

 dust from settling on the surface of the water. The slightly un- 

 even rim of the bell-glass seems to afford sufficient space between 

 itself and the glass cover for the necessary supply of air. It is 

 placed upon a hall-table, where it receives only a moderate supply 

 of light, and direct sunshine only on very rare occasions, when the 

 sun is near to the horizon. 



It was originally filled from the River Lea, and it has not since 

 been found necessary to change the water, but small quantities 

 have from time to time been added to compensate for evaporation. 

 Various kinds of water-weeds collected in the neighbourhood were 

 afterwards placed in it. Amongst these the hornwort ( CeratophyUuni 

 demersum) appears to be much in favour with large numbers of the 

 Infusoria, which very freely attach themselves to it. A small 

 piece of this weed which appeared to have floated down the Lea 

 was found to abound with great numbers of the delicate forms of 

 the " collared monads " (Choano-flagellata). Another favourite 

 weed, jRiceia fliiitans, which in small branched fragment-like por- 

 tions floats upon the surface of the water, was found in a pond 

 near Broxbournebury Woods, but it does not appear to be very 

 common in the neighbourhood. Another very useful weed for the 

 aquarium, the water-milfoil {Myriophyllum spicatum), is compara- 

 tively common. 



The American water-weed (Anacharis AUinastrum) is a desirable 

 acquisition, both on account of the foothold which it oflters to 

 numerous animalcules, and for the beautiful illustration its leaves 

 so readily aftbrd of the circulation in their cells. The common 

 duckweed [Lemna tumor), to the slender rootlets of which many of 

 the Infusoria may be fovmd attached, and the curiously-formed 

 ivy-leaved duckweed {Lemna trisulca), which has also been found 

 near Hertford, biit is by no means common, may be added. 



Amongst the various forms of microscopic animals which I have 

 from time to time found in this aquarium the following may be 

 mentioned. 



