LARVAE OF ARBACIA PUNCTULATA 



399 



ment of numerous heavy processes in the posterior region. Fusion of the arm- 

 rods inhibited. Irregularity of structure. In d, figures 113 and 116, a typical 

 pluteus-like form is not attained. This is in marked contrast to the solutions 

 in which isotonic NaCl is substituted for portions of the sea-water. In the 

 latter, arm-length is increased in proportion to body-length. 



