Mr. R. Warington^s Notes on Animals in small Aquaria. 3G9 



traordinary change gradually came on which had been observed 

 in the others, and after lingering for seventeen days they all 

 died. On carefully scrutinizing the different parts of the tank 

 with a magnifying-glass, my attention was at once arrested by 

 observing the enormous numbers of the Hydra fusca which were 

 present, particularly on the parts of the aquarium where the fish 

 had been accustomed to feed; that is, along the water-line 

 towards the light, at the base of the plants of Vallisneria spiralis, 

 about half an inch above the gravel, and on the whole of the 

 rock-work around the space where the minnows delighted to 

 hide ; here they might have been seen stretching out from the 

 sides, hanging down from the top, in fact in eveiy possible 

 direction — here then was a solution of all the evil. It now be- 

 came a question how these pests were to be eradicated, and after 

 canvassing in my mind a variety of suggestions, I determined to 

 endeavour to remove them individually, and by this means they 

 were speedily got rid of; from fifty to a hundred being taken 

 out daily. The method by which this operation was effected was 

 as follows : — A long glass capillary tube open at both ends was 

 introduced into the water, having the finger kept tightly over the 

 upper orifice, while, with the edge of the lower opening, the 

 polype was detached from its hold ; the moment this was effected 

 and the hydra began slowly to fall through the water, the finger 

 was removed, and the water with the polype was thus rapidly 

 driven into the tube by the pressure of the external column of 

 water ; on replacing the finger the contained water and polype 

 were removed. By persevering in this course they were caught 

 with the greatest rapidity and dropped into another vessel before 

 they had time to attach themselves to the interior of the tube, 

 falling through the water like a miniature parachute. When 

 situated in places where this mode of capture could not be em- 

 ployed, as on the leaves of the Vallisneria, or on the under sides 

 of the rock-work, they were pulled off with a jerk by means of a 

 small pair of forceps. In this manner between four and five 

 hundred polypes were removed from a small aquarium holding 

 about six gallons of water. Since this some small carp and also 

 minnows have been placed in the same water, and have continued 

 now for upwards of sixteen months in perfect health. 



It is a curious problem as to the manner in which this de- 

 struction of life was brought about ; my own impression is that 

 the hydras seized on the minnows whenever their extended ten- 

 tacula were touched by the swimming fish, — stinging them, and 

 causing a great degree of irritation ; and that the polypes were 

 torn from their position by the greater strength of the fish and 

 carried to their places of retreat, where, by consequence, the 

 mischief was continually accumulating. A similar removal from 



Ann. &; Mag. N. Hist. Ser. 2. Vol. xiv. 34 



