FIG. 22.--Astacus fluviatilis.--A longitudinal section of the body to show the principal muscles and their relations to th exoskeleton (nat.size). a, the vent; add.m., adductor muscle of mandible; e.m., extensor, and f.m., flexor muscle of abdomen; oes, oesphagus; pcp, procephalic process; t, t', the two segments of the telson; XV-XX, the abdominal somites; 1--20, the appendages; x, x, hinges between the successive abdominal somites.
[Editor's note: illustration is reproduced here approximately twice the size of the woodcut in the book.]
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