BEGAPODA. 293 



310 abdominal feet ; the conipound eyes are large and usually 

 sessile, and the carapace is often armed with a long dorsal 

 and frontal spine. Fig. 260 represents the Zoea, or larva of 

 the common shore crab {Cancer irroratus Say). After sev- 



Flg. 260. — Zo8a of the common Crab. Cancer. Much enlarged.— After Smith. 



eral moults, the thoracic legs appear, the mouth -parts 

 «hange 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 

 ^oSa and Megalops conditions, the body becomes more bulky, 

 more concentrated headwards, and the crab descends to the 

 bottom and hides under stones, -etc. 



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 Zoea, while the remarkable concentra- 

 tion of the parts headwards, seen in the crabs, is a great 



