


BARBADOS-ANTIGUA EXPEDITION 185 
that they may be sensory perhaps with a function similar to 
that of the osphradia of certain mollusks. 
Tt seems evident that this upper portion of the branchial 
chamber is modified for the purpose of breathing air, the high 
vascularity of the limiting membrane and the villi-lke tufts in 
the dorsal portion being almost certainly for this purpose. The 
conspicuous S-shaped tube may be really an immense sinus in 
lieu of a branchial blood vessel, opening into the body cavity 
not far from the heart. The gills proper occupy the lower part 
of the branchial cavity, being packed away just below the shelf- 
like process from the branchiostegite, and lying in a horizontal 
plane; the upper edges of the very numerous gill-plates forming 
a sort of paving to the upper part of the chamber. Resting 
just on these upturned edges of the gill lamelle is a much flat- 
tened thin chitinous blade-like plate with its edges fringed with 
long hairs greatly extending the surface of the plate. It reaches 
the entire lengh of the chamber and its anterior end 1s attached 
to the base apparently of the second maxilla which, by its move- 
ment, causes the plate to sweep back and forth over the up- 
turned edges of the gill lamella. The whole structure is in fact 
a modified secaphognathite, a delicate brush which applies water 
to the surface of the gill plates. The gills themselves, six in 
number, are not attached to the walking legs as in many deca- 
pods, but to the floor of the branchial chamber just above the 
bases of the legs. Thus the movement of the gills within the 
ehamber characteristic of many crustaceans is not possible here. 
Instead of this, it seems evident that the water is brushed over 
the gills by the blade-like structure just described. Upon lift- 
ing up the gills it is seen that there is a similar brush-like plate, 
more strongly bent in a horizontal plane, and with perhaps a 
fringe of longer hairs, attached to the base of the third max- 
illiped which by its movements sweeps this delicate brush over 
the lower edges of the gill lamella. Thus these two brushes 
apply the water to both the upper and lower edges of the 
numerous gill-plates, which are themselves stationary. A very 
thick matting of hair is found at the base of the third maxilliped 
near where the brush-like blade is attached. Still a third, but 
very much smaller, brush is found under the most anterior gill, 
which is tucked away beneath the S-shaped tube and against the 
