408 REPORT OF THE COMMISSIONER OF FISHERIES. 
seven pairs of appendages, which are usually designated as the first 
and second antenne, the mandibles, the first and second maxille, and 
the first and second maxillipeds, the latter being provided with long 
plumose hairs and used as the principal organs of propulsion as the 
animal swims through the water. The other thoracic appendages 
of the adult crab—namely, the third maxillipeds and the five pairs of 
legs—are represented only by a series of buds lying on each side, 
almost concealed by the shell. The shell itself is very thin and so 
transparent that the heart, the intestine, the, muscles which move the 
appendages, and all the other internal organs may be easily observed. 
The zowa sheds its shell a number of times, the bud-like rudiments 
of the third maxillipeds and the legs grow a little and the portion of 
the body which carries them becomes obscurely divided into segments. 
The abdominal feet or 
swimmerets make their 
appearance as pairs of 
buds on the ventral sur- 
face of the abdominal 
segments, and certain 
changes occur in the 
antenne and mandibles 
which cause these parts 
to resemble more closely 
the parts of the adult crab. 
For a number of molts 
the change of the larva is 
gradual, but after a time 
it sheds its shell and be- 
comes suddenly converted 
Cut 2.—Megalops form of Callinectes sapidus or some closely into US form which quite 
related crab. (After Brooks.) different from the zowa, 
and which is known as a 
megalops. The megalops differs from the zoxa in the following 
characters: 
(1) There are no lateral spines and the dorsal spine is very short. 
(2) The eyes are at the ends of very movable stalks. 
(3) The five pairs of legs are fully developed and are very, similar 
to those of the adult. 
(4) The gills have made their appearance above the bases of the 
legs, under the margins of the shell, but these margins are still free. 
(5) The maxillipeds are no longer organs of locomotion and there 
are three pairs. 
(6) While the larva is still able to swim, it also moves over the bot- 
tom by walking upon the tips of its legs, with a crab-like gait, very 
—S= 
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