86 THE AQUARIAN NATURALIST. 



central disc with from four to twelve horizontal, flat- 

 tened, cloven arms or lobes. An organ like an obtuse- 

 sided cluster-column projects from the middle of the 

 under surface, corresponding to the site of the pro- 

 boscis in other Medusae. Each lobe is cleft half-way 

 down. A cone in the centre at the bottom of the 

 cleft is surmounted by a black speck, which a powerful 

 magnifier shows to consist of a number of smaller 

 specks on a lighter ground. 



For the most part, the existence of the cloven Me- 

 dusa is very transitory. It appears unexpectedly, and 

 in a few days it decays or vanishes, though occa- 

 sionally obtained directly from the sea. Sir J. Dalyell 

 was led to remark that they had been chiefly observed 

 in vessels containing the Hydra tuba, and that when 

 removed they were frequently replaced by others; 

 nevertheless, no visible spawn, fragments, or other 

 elements to which their origin could reasonably be 

 ascribed, were ever distinguishable. He observed, 

 moreover, that they occur in the greatest abundance 

 in March, their appearance dating from the beginning 

 of February, during forty or fifty days ; and that they 

 are not to be seen from that season throughout the 

 rest of the year. 



Eight of these Medusae being observed on February 

 6th, in a vessel containing many specimens of the 

 Hydra which had been long under observation, they 

 were removed a day or two subsequently, as they were 

 conjectured to have been introduced in a replenish- 

 ment of sea- water; but they were soon succeeded 

 by others appearing in the same vessel on the 14th 

 and 15th. Meantime Sir John had remarked a con- 



