REPEODUCTIOX OF ACALEPHS 



875. 



most complete above, ami the upper discs usually presenting some 

 increase in diameter ; and whilst this is taking place the edges of 

 the discs become divided into lobes, each lobe soon presenting the 

 cleft with the supposed rudimentary eye at the bottom of it, which 

 is to be plainly seen in the detached Medusa? (fig. 665, C). Up to 

 this period, the tentacles of the original polype surmount the highest 

 of the discs ; but before the detachment of the topmost disc, this 

 circle disappears, and a new one is developed at the summit of the 

 bull) which remains at the base of the pile. At last the topmost 

 and largest disc begins to exhibit a sort of convulsive struggle ; it 



<* 





'i<;. 004. I, two Hi/il rir tii/iif [Scyphistoma-siage] of ('//mica 

 <-iipiU(it<i, with tw<> hi, in undergoing fission (jStfrofeiZa-stage). 

 II, a and b of fig. I three days later. In o the tentacles are 

 developed beneath the lowest of the Ejtlnjrcr, from the stalk 

 of the Strobild, which will persist as a Hydra tube. (After 

 Van Beneden.) 



becomes detached, and swims freely away; and the same series of 

 changes takes place from above downwards, until the whole pile of 

 discs is detached and converted into free-swimming Medusa 1 . But 

 the original polypoid body still remains, and may return to its 

 original polype-like mode of gemmation, becoming the progenitor of 

 a new colony, every member of which may in its turn bud off a pile 

 of Medusa discs. 



The bodies thus detached have all the essential characters of the 

 adult Jfeditsce. Each consists of an umbrella -like disc- divided at 

 its edge into a variable number of lobes, usually eight ; and of a 



