THE LOBSTEK. 
347 
It may very naturally be asked, however, in what way these 
parts are known to be really similar though apparently dif- 
ferent? In two ways: (1) By development, as in the young 
they all appear in the form of small processes, alike in size 
and shape; (2) By the examination of other animals belonging 
to the same group as the lobster, and thus it can be shown that 
parts which in the lobster’s thorax are very unlike his swim- 
merets are, in other allied creatures, quite like them ; short 
limbs, which in him are only limbs, in others are jaws alsOj 
while structures that in him are exclusively jaws, or feelers, in 
them are fully developed limbs. 
But now proceeding forwards through the cephalo-thorax, 
just as we proceeded backwards through the abdomen, we 
come first to a pair of limbs which are very unlike swimmer ets. 
Each consists of a series of joints, the basal one of which is the 
protopodite, indeed — but what are the rest? Here we must 
again have recourse to development, which tells us that in the 
young each limb had both exopodite and endopodite, but that 
as the adult condition is obtained the former aborts, so that the 
limb we are looking at consists really of a much elongated and 
segmented endopodite only. 
The limbs forming the next pair in advance are quite like 
those just described, except that each sends upwards from near 
its base a delicate and altogether new structure, which is termed 
the epipodite, or upper footlet, and serves to keep the gills 
apart from each other. All these thoracic limbs, however, end 
in a simple point, but each limb of the pair next in advance, 
otherwise, like the preceding, exhibits a further complication 
at its end, in that it is furnished with a claw (chela). This 
claw is formed by an outgrowth from one of the distal 
corners of the penultimate segment of the limb, and then 
the ultimate joint bites against this production of the penul- 
timate one. A limb so furnished is termed chelate. The next 
pair of limbs is quite like the last, and the one in front again is 
quite similar, except for the much larger size, for the fifth pair 
of thoracic limbs (counting forwards) constitutes the great claws. 
We now come to a great change, for the three pairs of limbs 
in front of the great claws are termed maxillipedes (foot-jaws). 
Each of these consists of protopodite, exopodite, endopodite, 
and epipodite, and in the hindmost pair the endopodite shows 
by its limb-like structure its essential similarity to the locomo- 
tive endopodites behind it, while its basal joint is very hard, 
sharp, and cutting, like a jaw. The exopodite, though present, 
is small. Here terminate the appendages which belong to the 
thorax, what follow appertain to the head. The hindmost of 
these is termed the second pair of maxillae, or jaws, and each such 
maxilla is of small size and delicate structure, but consists of a 
B B 2 
