LARVAE OF ARBACIA PUNCTULATA 



343 



The control specimens, a, underwent a rapid early growth 

 which resulted in a size at the age of 24 hours more than twice 

 that of the average. The maximum point on their growth- 

 curve occurred at an age of 96 hours, followed by a steady 

 diminution in size. At the close of 144 hours the arms were 

 shortened to a small fraction of their previous length (fig. 23), 

 and on the following day practically nothing remained of the 



Plot 3 



Plot 4 



skeleton except the body-rods with greatly reduced ventral 

 branches and dorso-ventral connectives (fig. 25). 



In comparing the growth-curves of the specimens in the 

 various solutions, we find that a primary inhibition of growth 

 occurs in the diluted sea-water, increasing in intensity in pro- 

 portion to the dilution of the medium. A secondary read- 

 justment occurs, however; consequently the specimens in h, 



