78 THE PHYSIOLOGY OF TH:ii COMMON CRAYFISH. 
fine straight hairs, or sete (F), whence a narrow stem (st) 
proceeds. At its upper end this stem divides into two 
parts, that in front, the plume (pl), resembling the free 
end of one of the gills just described, while that behind, 
the lamina (J), is a broad thin plate, bent upon itself longi- 
tudinally in such a manner that its folded edge lies for- 
wards, and covered with minute hooked sete (G). The 
gill which follows is received into the space included 
between the two lobes or halves of the folded lamina 
(fig. 4, p. 26). Each lobe is longitudinally plaited into 
about a dozen folds. 'The whole front and outer face of 
the stem is beset with branchial filaments ; hence, we may 
compare one of these branchie to one of the preceding 
kind, in which the stem has become modified and has 
given off a large folded lamina from its inner and 
posterior face. 
The branchie now described are arranged in sets of 
three for each of the thoracic limbs, from the third 
maxillipede to the last but one ambulatory limb, and 
two for the second maxillipede, thus making seventeen 
in all (8 x 5 +2=17); and, between every two there is 
found a bundle of long twisted hairs (fig. 17, A, cz.s; D and 
E), which are attached to a small elevation (¢) on the basal 
joimt ofeachlimb. These coxopoditic sete, no doubt, serve 
to prevent the intrusion of parasites and other foreign 
matters into the branchial chamber. From the mode 
of attachment of the six branchie it is obvious that they 
must share in the movements of the basal joints of the 
vyvaes 
