114 ZOOPHYTES. 



sented Plate XX. figs. 5, 25, was then nearly equal, when 40 and 

 50 days old respectively. It is seldom, however, that any can be pre- 

 served so long. The whole individuals of a numerous colony perish suc- 

 cessively. Their motion relaxes ; it becomes feeble and laboured ; they 

 cease to ascend ; and remaining at the bottom, their lobular arms closing 

 over the disc, the whitened colour and globular shape show them like 

 seed-pearls, when they languish and die. 



Sometimes, while still somewhat transparent, they disappear from 



amidst the water. 



Though occasionally recovered directly from the sea with other col- 

 lections, I was led to remark that they had been chiefly observed in vessels 

 containing the Hydra tuba or Sirolila of M. Sars, and that, when removed, 

 they were frequently replaced by others. But I could find no visible 

 spawn, fragments, or other elements, to which I could reasonably ascribe 

 their origin : nor were any Medusae ever to be seen bearing the most re- 

 mote resemblance to them. 



Then and afterwards I found their greatest abundance in March ; 

 that they occur from the beginning of February, during 40 or 50 days ; 

 that they are not to be seen from that season, at least in captivity, through- 

 out the rest of the year, in Scotland. 



Many of the rules and principles which determine the multiplication 

 of the highest orders, also extending to the lower tribes of animals, may 

 suggest some analogies here. 



Eight of the Medusae being observed on February 6, in a vessel with 

 many specimens of the hydras which had been long under observation, 

 they were removed a day or two subsequently. I conjectured them to 

 have come in a replenishment of sea-water on the first of the month. 

 These were succeeded by others appearing in the same vessel on the 14th 

 and 15th. I had remarked a convulsive motion among the tentacula of a 

 Hydra on the evening of the 14th, apparently from a Medusa having been 

 entangled there. The like occurred next morning, when one was libe- 

 rated. 



Similar convulsive motion agitating the same hydra during the 16th, 

 it was brought under closer inspection ; for, unable to discover the like 

 spasmodic demonstration among its companions, at least 100 in number, I 



