198 POPULAR HISTORY OF THE AQUAPvIU^I. 



parasitic sorts are taken from the fish to which they adhere. 

 They abound in water which we daily drink, and which 

 i]uenches the thirst of our cattle. They are believed to be 

 of great use in the economy of Nature, in ventilating the 

 water, especially the standing pools, which might otherwise 

 soon become putrid, while they give food to many marine 

 and fresh-water animals. By some authors they are consi- 

 dered, as a class, to be vegetable feeders, but actual obser- 

 vation seems to contradict this, especially in reference to 

 the Oypricles. " In a vessel," says Dr. Baird, " in which I 

 have kept full-grown Chirocephali there were mixed with 

 them many specimens of the Cypris tristriata. In a few 

 days the Chirocephali might be seen to become languid in 

 their movements, and assume an unhealthy appearance. The 

 Cyprides had become their deadly enemy. They might be 

 seen ever and anon to fasten themselves to the delicate feet 

 of the poor Chirocephali, and wofnlly impede their course 

 through the water ; and when, either from these annoyances 

 or from any other cause, they ceased to be able to move 

 with any degree of rapidity, hosts of these little carnivora 

 might be observed to attack them before life was extinct, 

 anticipathig as it were their victim^s death. Then, when 

 life had fairly ceased^ they rioted, as it were, upon their 



