266 
bui,le;tin of thf bureau op fisheries. 
DEVELOPMENT OF THE GREAT FORCEPS. 
How has the differentiation of the great claws been brought about? It is easy to 
follow the history of their development molt by molt from the first lg,rval stage onward. 
This history clearly shows that the toothed claw represents an original or an older 
type, and that the crusher claw was later developed by a modification of this primitive 
pattern. 
In the first larval stage of the lobster the future big claw (fig. 14) is distinctly of the 
embryonic type, relatively short and thick, and armed with few tactile bristles, its tips 
being drawn out, as it were, into 
long sharp-pointed spines. The 
dactyl, which bears the longer 
and straighterspine, is larger than 
the undeveloped index. This in- 
equality is much more marked in 
the smaller chelipeds, where the 
index appears as a bud-like out- 
growth, setate and bearing one or 
more stiff, barbed, or serrated 
bristles (fig. 2). 
In the second and third larvae 
(fig. 41 and 42) the claws become 
broader and more voluminous, 
while their spinous tips are re- 
duced and both index and dactyl 
are curved. 
In the fourth stage (fig. 9 and 
pi. xxxi) the great chelipeds sud- 
denly become very conspicuous, 
bearing long slender forceps which 
now for the first time serve as 
organs of prehension with marked 
success. The jaws of the forceps 
. me snore iscnium UA wiin iree joint at luture oreaKing plane UA ana i , j ^ i 
base of swimming branch (£1). Compare with text figures 6 and 9. are slender, dentate, and tufted 
with tactile hairs. The condition 
of symmetry, with this general structure, on right and left sides, continues through the 
fifth and in some cases up to the seventh or eighth stage, when the first traces of asym- 
metry begin to appear, though not necessarily apparent to the naked eye. (Fig. 15 and 
16.) By the ninth stage, when a total length of about one and one-quarter inches has 
been reached, the differentiation of the crusher claw is easily recognizable, but the 
changes registered at each molt are slight. In the account which follows we shall con- 
sider in more detail the beginnings of asymmetry and the development of the teeth 
and tubercles which characterize the two types of big claw in the adult animal. 
