101 

 STUDY XX A . 



THE PERMANENCE OF THE SCYPHISTOMA STAGE 



OF AUEELIA. 



Three years ago, in 1893, large numbers of the Scyphistoma or 

 Hydra-tuba stage of the Medusa Aurelia aurita appeared on boulders 

 in several of the tanks of the Jersey Biological Station. Since then, 

 colonies produced from these individuals have been permanent on the 

 same stones. The continuity has been absolute, individuals having 

 practically been under daily observation since their first appearance. 



Under favourable conditions of food supply and temperature the 

 increase in their numbers by budding was very rapid. The buds 

 grew out from any part of the body ; lengthened each into a 

 stolon that crept along the rock till some quarter inch away from the 

 parent, then made adhesion by a part that would finally become the 

 basal disc, quickly budded forth a ring of tiny tentacles, opened a 

 mouth aperture and finally constricted and then cut through the bond 

 with the parent, the two parts of the stolon being absorbed by the 

 respective individuals. Sometimes a Scyphistoma would give off two 

 or even three stolons at the same time, and as the growth of the young 

 individuals from these outgrowths is sometimes very rapid, the vast 

 increase of the colonies is comprehensible. No wonder that Aurelice 

 some seasons swarm in countless millions in our seas ! 



While this process of multiplication goes on very rapidly during 

 the greater part of the year, towards the end of January and the 

 beginning of February a second mode of reproduction, strobilation, 

 takes place. This, as is so well known, is the constriction of the 

 polyp-like body of the scyphistoma into short-armed plate-like divi- 

 sions or discs, arranged in a manner similar to a rouleau of coins. 

 One by one the discs broken off from the stock, float away as ephyrse 

 little pulsating plates that by gradual change and growth, pass 

 imperceptibly into the adult sexual medusa, the female producing 

 ciliated embryos that, after a short free-swimming existence, settle 

 down, form tentacles and mouth and assume the alternate sexless or 

 Scyphistoma-stage. 



Every year since 1893, my captive colonies have thrown off their 

 ephyrae,but the individuals never assume the polydisc or typical 

 form, usually I believe most common in strobilating individuals 

 in the open sea. Mine have all been monodisc strobilae, producing 

 not a rouleau of ephyrse discs, but each a single ephyra. This I am 

 inclined to attribute to a lower vitality than is possessed by those in 

 the sea, induced by the smaller food supply available in the tank 

 water, which is to a large extent filtered prior to admission to the 

 tanks. 



Apparently a colony can exist indefinitely ; the specimens I now 



