respiration. They consist, exactly as described by Leydig in the
Daphniae, of an outer and inner lamina, the space between which is
traversed by numerous transverse partitions dilated at their ends; the
spaces between these partitions are penetrated by a more abundant flow
of blood than occurs anywhere else in the body of the Zoea. To this may
be added that a constant current of fresh water passes beneath the
carapace in a direction from behind forwards, maintained as in the adult
animal, by a foliaceous or linguiform appendage of the second pair of
maxillae (Figure 18). The addition of fine coloured particles to the
water allows this current of water to be easily detected even in small
Zoeae.

(FIGURE 17. Zoea of a Marsh Crab (Cyclograpsus ?), magnified 45 diam.

FIGURE 18. Maxilla of the second pair in the same species, magnified 180
diam.)

The Zoeae of the Crabs (Figure 17) are usually distinguished by long,
spiniform processes of the carapace. One of these projects upwards from
the middle of the back, a second downwards from the forehead, and
frequently there is a shorter one on each side near the posterior
inferior angles of the carapace. All these processes are, however,
wanting in Maia according to Couch, and in Eurynome according to
Kinahan; and in a third species of the same group of the Oxyrhynchi
(belonging or nearly allied to the genus Achaeus) I also find only an
inconsiderable dorsal spine, whilst the forehead and sides are unarmed.
This is another example warning us to be cautious in deductions from
analogy. Nothing seemed more probable than to refer back the beak-like
formation of the forehead in the Oxyrhynchi to the frontal process of
the Zoea, and now it appears that the young of the Oxyrhynchi are really