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What is the typical Structure of a Crayfish Appendage ? 



A basal piece, the protopodite, bearing two branches,, 

 an inner endopodite and an outer exopodite. 



Which are the Sensory Appendages of Astacus, and where 

 Ure they situated ? Explain their Structure. 



The short first antennae or antennules and the long 

 second antennae or feelers. Both pairs project from th& 

 fore- part of the head, in front of the mouth. 



The antennules have each a three- jointed protopodite 

 bearing a filamentous and many- jointed exopodite and a 

 similar endopodite. On the upper surface of the basal 

 joint of the protopodite there is a minute sac fringed with 

 delicate setae, the otocyst, an auditory and balancing 

 organ. Some of the setae fringing the exopodite have- 

 an olfactory sense. 



The antennae have two-jointed protopodites (basipodite 

 and coxopodite). The exopodite is a short scale (th& 

 squame) ; the endopodite is long and filamentous. On 

 the basal joint of each protopodite there is an opening of 

 a kidney or " green gland." 



Name the Appendages of the Crayfish which have a Masti- 

 catory Function, and describe their Parts. 



The mandibles ... Protopodite is a hard-toothed 

 gnathobase. Endopodite is a 

 small three- jointed palp. Exo- 

 podite is absent. 



W ist Maxillae ... Protopodite forms a blade-like 

 bipartite gnathobase. Endo- 

 podite is a small filament. 

 Exopodite is absent. 



2nd Maxillae ... Protopodite forms a blade-like 

 quadripartite gnathobase. En- 

 dopodite is filamentous. Exo- 

 podite, joined to epipodite, forms- 

 the " baler " or scaphognathite 

 (a respiratory organ). 



