DECAPODA. 293 
- no abdominal feet ; the compound eyes are large and usually 
sessile, and the carapace is often armed with a long dorsal 
and frontal spine. Fig. 260 represents the Zoéa, or larva of 
the common shore crab (Cancer irroratus Say). After sev- 
Fig. 260.—Zoéa of the common Crab. Cancer. Much enlarged.—After Smith. 
eral moults, the thoracic legs appear, the mouth - parts 
change from swimming-legs to appendages fitted for pre- 
paring the food to be swallowed and digested. This stage 
in the short-tailed Decapods or crabs, is called the Mega- 
lops stage (Fig. 261); certain immature crabs having been 
mistaken for and described as mature Crustacea, under the 
name Megalops. After swimming about the surface in the 
Zoéa and Megalops conditions, the body becomes more bulky, 
more concentrated headwards, and the crab descends to the 
bottom and hides under stones, ete. 
The development of the individual crab is, in a general 
sense, an epitome of the development of the order. In the 
lowest genera, as in Cuma and Mysis, the form is some- 
what like an advanced Zoéa, while the remarkable concentra- 
‘tion of the parts headwards, seen in the crabs, is a great 
