NATURAL HISTORY OF AMERICAN LOBSTER. 
223 
great chelipeds and the first pair of swimmerets. The complex and varied relations 
of the successive somites and appendages of the lobster in the larval and adult state are 
outlined in table 4. 
In their type form (fig. 2 and pi. xxxvi, fig. 5) the appendages consist of an inner 
and outer branch borne on a basal stem, known respectively as endopodite, exopodite, 
and protopodite. The protopodite is composed of two segments, a proximal coxa, or 
coxopodite, and distal basis or basipodite. The coxa of each limb from the maxillae to 
the fourth pair of pereiopods (somites v-xiii) bears a hairy respiratory plate or epipodite, 
from which rises a gill or podobranchia on all but the first two of these somites. The 
primitive type of crustacean limb was probably biramous, since in the course of develop- 
ment we frequently find the uniramous condition produced by loss of the more transi- 
tory exopodite, and further, since the foliaceous form of appendage of the lower branchio- 
pod Crustacea is secondarily assumed by certain of the mouth parts of the lobster and 
other decapods. The undivided form of limb is permanently preserved in metameres i 
and x-xv, in the last of which the appendage is modified in the two sexes to perform 
distinct functions. The origin of the two-branched antennules will be considered 
presently. The exopodite is frequently abortive, or multiarticulate and elastic, as 
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