") and the first rudiment of the future
flagellum is often already recognisable. Of natatory feet (afterwards
maxillipeds) only two pairs are present; the third (not, as Spence Bate
thinks, the first) is entirely wanting, or, like the five following
pairs of feet, present only as a minute bud. The tail, of very variable
form, always bears THREE pairs of setae at its hinder margin. The Zoeae
of the Crabs usually maintain themselves in the water in such a manner
that the dorsal spine stands upwards, the abdomen is bent forwards, the
inner branch of the natatory feet is directed forwards, and the outer
one outwards and upwards.
(FIGURES 19 TO 23. Tails of the Zoeae of various Crabs.
FIGURE 19. Pinnotheres.
FIGURE 20. Sesarma.
FIGURE 21. Xantho.
FIGURES 22 AND 23 of unknown origin.)
It is further to be remarked that the Zoeae of the Crabs, as also of the
Porcellanae, of the Tatuira and of the Shrimps and Prawns, are
enveloped, on escaping from the egg, by a membrane veiling the spinous
processes of the carapace, the setae of the feet, and the antennae, and
that they cast this in a few hours. In Achaeus I have observed that the
tail of this earliest larval skin resembles that of the larvae of
Shrimps and Prawns, and the same appears to be the case in Maia (see
Bell, 'Brit. Stalk-eyed Crust.' page 44).
Widely as they seem to differ from them at the first glance, the Zoeae
of the Porcellanae (Figure 24) approach those of the true Crabs very
closely.
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