NATURAL, history OP AMERICAN EOBSTER. 
271 
even sharper than before and retain their periodic character. The spines of the lock 
forceps are also noticeably larger for a time at least. Then follows a characteristic 
process of concentration and fusion in the spines of the future crusher claw (fig. 24, c. s., 
and fig. 25, d.), which eventually leads to the reduction of their number. The crushing 
tubercle is thus formed by the fusion of a greater or lesser number of spines, like those 
of the toothed claw in the fourth to sixth stages. 
In the light of this process are to be explained the “transition forms” which Przi- 
bram found to arise in the course of regeneration of the crusher claw, showing the knobs 
as fusing masses of teeth. The occurrence of such transitional stages has also been 
mentioned by Stahr and Emmel. 
In the adult cracker claw (pi. xeiii, fig. 2 and 3 ) the propodus bears two large 
and six or more smaller tubercles. The big proximal tubercle {p (L), fig. 25) repre- 
JT M IV 
Figs. 23 and 24.— Serrate margins of daws shown in figures 21 and 22, in regions marked a and b, and corresponding 
to periods ii-iv. Two perfect periods of eight sharp spines appear in the future lock forceps, and interpolations with 
fusions of teeth (c s) in the future crusher. 
sents mainly the lock spine of the toothed claw, with the addition of lesser elements, 
while the great distal tubercle (d.) is composed of a fused mass of upward of thirteen 
spines, embracing the whole of the third and a part of the second periods. The dactyl 
of the crusher also possesses two tubercles of greater size, which close over the intervals 
between the “molars” of the propodus, besides a dozen or more small ones, resulting in 
each case from the fusion of several spines. There is also a small rounded tubercle on 
this segment at its proximal end and below the serial line. 
The final differentiations established between the great erusher and lock forceps 
are illustrated by a perfect set of typical claws from a hard-shelled lobster which must 
have weighed approximately 12 pounds. In all measurements excepting length this 
crusher greatly exceeds its fellow, being one-third broader, weighing twice as much (in 
the dry shell), and having more than double the cubic capacity. In animals of adult 
size the slenderer claw has often a slight advantage in length over the more powerful 
