No. 605] SHORTER ARTICLES AND DISCUSSION 309 



formed across the surface of the break. Five days later, June 

 25, the protecting membrane had hardened, so that it could not 

 be dented with the point of a scalpel. No further change could 

 be noted until after the molting, which occurred four days later, 

 June 29. The casting occurred at night, and the next morning 

 the new shell showed no signs of any wound. By one o'clock a 

 very slight hump appeared, and by ten o'clock at night a little 

 rudimentary spine 2 mm. in length had formed. The next morn- 

 ing another millimeter had been added to its U^ngtli. :\[eantime 

 the normal spine had increased 1.5 nun. in length. No further 

 growth followed before the new sliell had hardened. 



Sixteen days later, July 15, another molt occurred. As before, 

 the old shell was cast at night and by the following morning the 

 regenerating spine had added 2 mm. to its Inigtli. luMng now .") 



by the hardening of the new sliell. l)ut the folal l.Migili «m" the 

 spine was at this time 7 mni. The spnie now showed a shari) 

 point an.l aUo .i Omhr lar^iMl M)niir . .mom lik- tha^t of the iinnnal 



length, .showing that, while the whole animal was growing, the 



