No. 605] SHORTER ARTICLES AND DISCUSSION 310 



regenerating part was increasing at a much faster rate than 

 other parts. 



Thus in the period of twenty-seven days during which the ani- 

 mal was under observation, it had undergone two molts and had 

 regenerated a missing rostral spine of normal form, 7 mm. in 

 length, while the normal spine had added 2.5 mm. to its length 

 in the same period. These results show that the period between 

 molts for this animal under laboratory conditions is six- 

 teen days; that a rostral spine of normal form can be regen- 

 erated ; and that the rate of this regeneration was nearly 

 three times the rate of normal growth of a similar spine during 

 the same period. 



A. C. WALTON 



HARVARD UNIVERSITY 



