346 



THE CRAYFISH 



hatched in the form of a free-swimming larva, to which this 

 name is applied, characterised by the presence of three 

 pairs of appendages, used for swimming and becoming the 



Fig. 91. — Later embryo of Fresh-water Crayfish, from the ventral 

 aspect ; the abdomen (ai) is folded down over the cephalothorax, so 

 that its dorsal surface faces the observer, and the lelson {T) reaches 

 nearly to the mouth. 



The following appendages are indicated : A, eye-stalks ; a', anten- 

 nules ; a^, antenna; ; m, mandibles ; mx^, mx^, maxillae ; /. i-(. 8, 

 thoracic appendages (maxillipedes and legs). 



At the sides of the thorax are seen the edges of the carapace (/s) : in 

 front of the mouth is the labrum (/), in front of the labrum the brain (^), 

 and at the base of the eye-stalk the optic ganglion {^0). 



(From Lang, after Reichenbach. ) 



antennules, antennae, and mandibles of the adult. In the 

 crayfish there is no free larva, and the nauplius stage is 

 passed through before hatching. 



The nauplius is gradually transformed into the crayfish by 



