Physiology of Regeneration 641 
the same as in normal sea-water. Sea-water diluted to 75 per 
cent its original strength produces a retarding effect on the power 
of regeneration, and.a dilution to 50 per cent is very injurious to 
the worms. 
14 The addition of MgCl, to the sea-water may produce a 
favorable or an unfavorable effect on the power of regeneration 
according to the amount employed. More than § cc. of a molec- 
ular solution may retard or even completely inhibit the regenera- 
tive process, whereas smaller quantities (5 cc. of 7 solution) may 
often be very beneficial both to the regeneration and growth of 
new segments. It is probable that the beneficial effect on the 
rate of regeneration produced by the addition of a small amount 
of MgCl, to the sea-water is not the outcome of a change in 
osmotic pressure alone. 
. 
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