309 



THE AMERICAN NATURALIST 



[VOL. LI 



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 length. Meantime 

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

 growth followed before the new shell had hardened. 



rryn. 



norm . 



FIG. 1. Prom a photograph of the left side of the head region of Panulirus 

 argus, showing (norm.) the normal, and (regn.) the regenerated rostral spine. 

 As the figure is reproduced from a photographic print, the picture is reversed, 

 the right spine appearing like a left one. 



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 length, being now 5 

 mm. long. By the next evening all growth had been stopped 

 by the hardening of the new shell, but the total length of the 

 spine was at this time 7 mm. The spine now showed a sharp 

 point and also a slight lateral compression like that of the normal 

 spine. At this casting the.normal right spine added 1 mm. to its 

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



