HEAD APPENDAGES 135 



and the endopodite is a small plate to their outer 

 side. There is no exopodite. 



III. The mandible consists of a very stout undivided 

 protopodite, forming the powerful jaw at the side 

 of the mouth ; and an endopodite, which forms a 

 small three-jointed palp, lying in a groove on the 

 front of the protopodite. 



Before removing the mandible, note the position of the two 

 pivots about which it turns, and the points of insertion of the 

 tendons of its abductor and adductor muscles. 



Immediately in front of the first maxilla and 

 behind the mandible is a small unjointed plate, leaf- 

 like in form. It is not regarded as a true appendage, 

 but as an outgrowth of the metastoma, which forms 

 the posterior and lateral borders of the mouth. 



II. The antenna consists of protopodite, exopodite, and 



endopodite, the last of which forms the long 



' feeler.' 



i. The protopodite consists of two joints ; the first, 



or coxopodite, being very broad, and projecting 



only very slightly from the surface of the head : 



on its ventral surface is a tubercle perforated 



posteriorly by the renal aperture. The second 



joint, or basipodite, is also short and stout, and 



bears the endopodite and exopodite. 



ii. The endopodite has two stout basal joints and a 



long slender many -jointed feeler. 

 iii. The exopodite is a stoiit sharp-pointed blade, 

 the scaphocerite. 



I. The antennnle is smaller than the antenna. 



i. The protopodite is three-jointed, the basal joint 

 being much the largest, and containing the 

 auditory organ, which opens on its dorsal 

 surface. The aperture is three-cornered, and 

 is guarded by a series of plumose setaa, which 

 extend across it from its outer lip. 



