Rate of Regeneration in Cassiopea xamachana. 93 



Magnesium salts in sea-water retard pulsation and reduce its rate, am- 

 plitude, and energy. The disk will pulsate at twice its normal rate in sea- 

 water minus magnesium. In a 1.6 per cent sea-water solution of MgCL the 

 disk pulsates slowly for half an hour and then stops. 



The medusae in the following regeneration experiments were subjected 

 to the influences of sea-water concentrated to two-thirds and three-fourths 

 of its original volume; or to sea-water diluted with distilled water, two 

 parts of sea-water to one of distilled and one of sea-water to one of dis- 

 tilled; or to sea-water solutions of NaCl". "S 3", and^" ; KC1-". "^ "^ and ," ; 

 CaCl, ;^. j^, and £ and MgCL '\ ;", and ;". The medusas were all cut as 

 shown in fig. 29. The margin of the removed piece included four of the 

 peripheral sense-organs and was made as near as possible of the same 

 proportional size in the several medusae.^ 



The regeneration of these medusae is shown 

 in tables 6 and 7, which have been arranged from 

 two experiments run at dift'erent times. In the 

 first column of these tables the solutions em- 

 ployed are listed; the second and fifth columns 

 contain the diameters of the individuals at the 

 times indicated, the third and sixth columns give 

 the exact amounts of regeneration that have 

 taken place in a radial direction from the middle 



of the cut surfaces ; the fourth and seventh cul- r .■ , 



Fig. 29. — Diagram of disk 



umns show the specific amounts of regeneration „ith straight cut remov- 

 from the difl:"erent individuals. These last '"g f"""- "f ''^ marginal 



fense-organs. 



amounts may be compared also as specific rates 



of regeneration per day, since all have consumed like periods of time in the 



regeneration process. 



The rates of pulsation of the niedu.s;e disks were retarded in all of the 

 solutions after the first several hours, the retardation being more marked in 

 some cases than in others. The pulsations were always, however, slower 

 than the controls. 



The animals in the sea-water concentrated to two-thirds its original 

 volume died within two days. Those in the three-fourths concentrated sea- 

 water were so weakened that they showed no beginning of regeneration 

 and were placed in normal sea-water after the third day. The diluted sea- 

 water solutions also had a decidedly depressing efifect. All niedusre in such 



' Those in table 6 treated with KCI - and MgClj - were small individuals, as indi- 



50 ° 40 



cated, and were cut in the dovetailed way shown in figure 10. This no doubt accounts 



in part for their apparently rapid regeneration, for it will be recalled that the deeper 



portion of a cut of this shape regenerates at a faster rale than a straight cut, such 



as that in figure 29. 



