1899-1900.] Report of the Microscopical Section. 125 
the cardiac, the posterior and smaller called the pyloric. 
The gullet opens directly into the floor of the cardiac chamber, 
and here the food which has not been sufficiently crushed 
and divided by the mandibles and other external grinding 
surfaces encounters another complicated set of crushing 
apparatus called the gastric teeth. These consist of two 
powerful lateral teeth and a median one, together with two 
accessory lateral ones, all actuated by muscles, so that they form 
avery complete mill, by which the food is so finely divided 
that it can be passed on to the pyloric chamber. The 
entrance to this chamber is still further guarded. In addition 
to the constriction of the side-walls, a projection something 
like a hood rises in the centre, and thus leaves only a narrow 
slit or opening on each side. These openings are again pro- 
tected by a fringe of delicate sete, which spring from the 
‘side walls, so that the entrance is closed to everything but 
‘the most finely divided particles of food. This part of the 
stomach is called the cardio-pyloric valve. There are other 
accessory valves, the function of the whole being to prevent 
any particles of food not sufficiently divided from entering 
the intestine. All such particles are understood to be 
ultimately ejected through the gullet. For a low power, of 
from 6 to 10 diameters, which enables the whole organ to be 
seen at the same time, the interior of the stomach of the 
crayfish is a beautiful microscopic object. 
The respiratory organs consist of gills, or branchiz, placed in 
a chamber on each side of the thorax. The part of the 
exoskeleton which forms the covering of these chambers is 
called the branchiostegite. On the tergal aspect the branchi- 
 ostegite forms a solid mass with the exoskeleton of the thorax, 
but on the ventral aspect it has a free edge, thus permitting 
free access to the surrounding water. In each of the 
branchial chambers there are eighteen functional gills, 
arranged in three sets, grouped around each of the thoracic 
limbs, except the first maxillipede and the last ambulatory 
limb. The following is the arrangement: attached to the 
basal joint of each of these limbs is a gill, six in number, 
ealled podobranchiz, while in the soft interarticular parts of 
these limbs are another set of six, called arthrobranchie; a 
little more to the interior of the branchial chamber is a set of 
