THE CRUSTACEA 



155 



legs, and is now of the form termed a Megalope. But 

 it still swims in the open, only it begins to frequent the 

 bottom a little. 



Finally it tucks its tail beneath the body and assumes 

 the Brachyumn or " short-tailed " true " crab " form 

 (Fig. 64). Its size during these changes ranges from a small 

 o to a capital in this type. 



All the Brachyura pass through these stages, only some 



A Ji C D 



Fig. 63. Development of Shore Crab. A. Eggs with enclosed 

 larvae ; B. just hatched Zoea ; C. Zoea, 2 to 15 days or so ; 

 D. Megalope stage. A, B, and C, about 20 diameters; D, about 

 10 diameters 



differences in slight structural detail marking the different 

 species. 



In the Macrura (prawn, lobster, etc.) there are not so 

 many changes, the young of these emerging from the egg 

 more or less on the plan of the parent, modification of the 

 various appendages only being needed to complete the form. 



There are, however, some exceptions, e.g. in the " craw- 

 fish " (Palinurus), etc. as we have seen, 



