660 RECORD OF CURRENT RESEARCHES RELATING TO 



occur partially. The tonic spasm continues progressively to increase 

 in severity, and gives the outline of the margin a very irregular form ; 

 the twitching contractions become weaker and less frequent, till at last 

 they altogether die away. Irritability, however, still continues for a 

 time, a nip with the forceps being followed by a bout of rhythmical 

 contractions. Death occurs in several hours in strong and irregular 

 systole. 



If the exposure to sea-water has only lasted two minutes, a similar 

 series of phenomena are presented, excejit that the spontaneous twitch- 

 ing movements supervene in much less time than twenty minutes. But 

 an exposure of even one minute may determine a fatal result a few 

 hours after the Medusa has been restored to fresh water. 



Contact with sea-water causes an opalescence and essential disin- 

 tegration of the tissues, which precisely resemble the effects of fresh 

 water upon the marine Medusai. When immersed in sea-water this 

 Medusa floats iipon the surface, owing to its smaller specific gravity. 



In diluted sea-water (50 per cent.) the preliminary tonic spasms do 

 not occur, but all the other phases are the same, though extended through 

 a longer period. In sea-water still more diluted (1 in 4 or 6) there is 

 a gradual loss of sjjontaneity, till all movement ceases, shortly after 

 which irritability also disappears ; manubrium and tentacles expanded. 

 After an hour's continued exposure intense rigor mortis slowly and 

 progressively develops itself, so that at last the bell has shrivelled 

 almost to nothing. An exposure of a few minutes to this _ strength 

 places the animal past recovery when restored to fresh water. In still 

 weaker mixtures (1 in 8 or 10) sjwntaneity persists for a long time, 

 but the animal gradually becomes less and less energetic, till at last it 

 will only move in a bout of feeble pulsations when irritated. In still 

 weaker solutions (1 in 12 or 15) spontaneity continues for hours, 

 and in solutions of from 1 in 15 to 18 the Medusa will swim about 

 for days. 



It will be seen from this account that the fresh-water Medusa,, is 

 even more intolerant of sea-water than are the marine sjDecies of 

 fresh water. Moreover the fresh-water Medusa is beyond all com- 

 parison more intolerant of sea-water than are the marine species of 

 brine ; for the marine species will survive many hours' immersion in 

 a saturated solution of salt. While in such a solution they are 

 motionless, with manubrium and tentacles relaxed, so resembling the 

 fresh-water Medusa shortly after being immersed in a mixture of 

 1 part sea-water to 5 of fresh ; but there is the great difference that 

 while this small amount of salt is very quickly fatal to the fresh-water 

 species, the large addition of salt exerts no permanently deleterious 

 influence on the marine species. 



We have thus altogether a curious set of cross relations. It 

 would appear that a much less profound physiological change would 

 be required to transmute a sea-water jelly-fish into a jelly-fish adapted 

 to inhab t brine, than would be required to enable it to inhabit fresh 

 water. Yet the latter is the direction in which the modification has 

 taken place, and taken place so completely that sea-water is now more 

 poisonous to the modified species than is fresh water to the unmodified. 



