NATURAIv HISTORY OF AMERICAN LOBSTER. 267 



In the fourth stage the great claws are not only symmetrical, but of the toothed 

 type. According to Emmel (96) the transition to the asymmetrical condition begins 

 in the sixth stage, but in the material studied as a basis for this account it was impossible 

 to detect any morphological differences until the seventh or succeeding stage. There is 

 doubtless some variation in this respect. It is true that at preceding periods the big 

 claws may differ in size or slightly in form as a consequence of molting or regeneration, 

 but without implying the differentiation in question. Again at the seventh stage these 



Fig. 15 and 16. — Left and right future toothed and crusher claws of lobster in eighth stage, seen from above. The claws are 

 of equal length, and the differentiation of the crusher is not apparent to the naked eye. Compare with figures 21 and 22. L, 

 lock spine; p, compound proximal tubercle of crusher claw. Enlarged about 34 times. 



claws may appear to the naked eye essentially alike in form and size. Thus, to give 

 a concrete example, a lobster in the eighth stage, measuring 19.75 milimeters, September 

 22, showed a rather striking similarity in the forceps, the dimensions of which were as 

 follows : 



Right claw (future cruslier): Millimeters. 



Length 7 



Breadth i. 7 



Left claw (future toothed forceps): 



Length 7 



Breadth j.. 4 



