258 HYDRACHNA. 



them. Among others taken subsequently from the same place was one 

 evidently in a fit, which remained so for some time, lying motionless while 

 removed to a different vessel. Next, the feet beginning to move, it re- 

 vived, and swam away. Another died after remaining long in a fit, 

 copiously discharging a reddish-brown liquid. 



Some anologies will be found quite as decided between the nature 

 of this and the Cancer tribe, rigorously circumscribed as such. 



Hydrachnae, so active throughout the day, seem to pass the night 

 in profound repose. Early in the evening the numerous tenants of a jar 

 of water are all seen motionless, resting on the neighbouring plants, or 

 sustaining themselves by contact with the side of the glass. There the 

 limbs are much contracted, and nearly in the same attitude as if clinging 

 to a plant. 



The common equisetum, or horse-tail, is useful as a place of repose 

 for the night, besides which, it is nibbled by these creatures during the 

 day. Its presence may be still farther beneficial, as a place of protection 

 from their mutual hostilities. At night, therefore, the general quiescence 

 proves a considerable difference from the nocturnal habits of most 

 aquatic, and especially most marine animals, rendering it the season of 

 their widest excursions, and their fiercest encounters. 



The repose of the Hydrachna is also influenced by the absence of 

 light, for it is uninterrupted while an apartment continues dark, but all 

 are aroused to action by its admission. Then their chief enjoyment is 

 sporting in the sunshine, and in their renovated element. 



Hydrachnae are among the most rapacious of living animals, bold, 

 fierce, and cruel, the natural and inveterate enemies of all their congo- 

 nera : they are no less hostile to each other, against which is waged a 

 perpetual war of extermination. Neither do they hesitate on attacking 

 such animals as are suitable to their appetites, though double the size of 

 the assailant. 



One species, let us provisionally denominate it IIydrachna ferox, 

 from its nature, dwelt in a small pond, in common with another species 

 not dissimilar, though perhaps of somewhat inferior dimensions, the back 

 stained with a yellow cross. Plate LXIX., figs 1, 2, natural size and 



