BREAKING UP OF " STROBILA" INTO MEDUSAE. 85 



activity, but at the end of that time they generally 

 begin to flag, and rarely survive more than a fortnight, 

 at which time their movements become very slow and 

 feeble, and then they vanish, leaving behind them no 

 perceptible trace. 



Long ago, says Sir John Dalyell, I had remarked 

 colonies of minute transparent animals swimming 

 in vessels of sea- water during the months of Feb- 

 ruary, March, and April. Their general aspect very 

 much resembled a flock of birds in distant flight, 

 as represented by landscape painters (PI. I. fig. 5, b) . 

 After being transferred to vessels free of other sub- 

 jects, they continued several days in activity and then 

 disappeared. I could not account either for their ori- 

 gin or their transience. They occurred only at rare in- 

 tervals, and always identically under the same form. 



More accurate inspection showed the alliance of such 

 creatures to that comprehensive genus the Medusa, 

 both in configuration and habits. But the date of their 

 appearance did not correspond with the wonted pe- 

 riodical ascent or arrival of that tribe to the surface 

 of our seas during the summer months indeed they 

 were met with as early as the 6th of February. 



The species of Medusa to which these little beings 

 belonged, is that long ago denominated by Baster 

 Medusa minutissima, and being, in fact, among the 

 more minute, it maybe rather considered a microscopic 

 object than otherwise. Its expansion is between one 

 and two lines, nor did it present any sensible growth 

 during the longest period (sixty days) of its sur- 

 vivance. 



This creature's body (PI. I. fig. 5,^} consists of a 



