168 THE MORPHOLOGY OF THE COMMON CRAYFISH. 
limbs, are spoken of as if they were totally different 
structures, under the name of branchie or gills. 
The flagellum or epipodite of the first maxillipede, 
however, is nothing but the slightly modified stem of a 
podobranchia, which has lost its branchial filaments; 
but the term ‘ epipodite’’ may be conveniently used for 
podobranchie thus modified. Unfortunately, the same 
term is applied to certain lamelliform portions of the 
‘branchie of other crustacea, which answer to the lamine 
of the crayfishes’ branchie ; and this ambiguity must be 
borne in mind, though it is of no great moment. 
On examining an appendage from that part of the 
thorax which lies behind the third maxillipede, say, for 
example, the sixth thoracic limb (the second walking leg) 
(fig. 46), the two joints of the protopodite and the five 
joints of the endopodite are at once identifiable, and so 
is the podobranchia; but the exopodite has vanished 
altogether. In the eighth, or last, thoracic limb, the 
podobranchia has ‘also disappeared. The fifth and 
sixth limbs also differ from the seventh and eighth, 
in being chelate; that is to say, one angle of the distal 
end of the propodite is prolonged and forms the fixed leg 
of the pincer. The produced angle is that which is 
turned downwards when the limb is fully extended 
(fig. 46). In the forceps, the great chela is formed in 
just the same way; the only important difference lies in 
the fact that, as in the external maxillipede, the basipo- 
dite and the ischiopodite are immoveably united. Thus, 
