12 PEOF. M. M. HAETOG ON THE 



Third joint longer, cylindrical, widening distally, with greater range of extension and 

 flexion ; on extensor ridge are in succession a plume and five hooked spines, getting 

 larger distally, and three others lie at extensor side of distal end. 



Fourth joint narrower, slender, oblong, hears seven hooks of various sizes, and round 

 apex inserted into a thin chitinous membrane, forming the apex of the limb. 



Proper Muscles of the Antenna. — Flexor, origin doubtful ; insertion on flexor side of 

 base of second joint. Extensor of third joint, from base of second to base of third joint. 

 Detaching muscles : one taking origin about the middle of the basal joint, going to the 

 insertion of the three terminal hooks of the third joint ; another, stouter, taking origin 

 a little beyond the last, and ending in the membrane forming the distal end of the limb, 

 on which are inserted the seven hooks. The action of these muscles must be to detach 

 the hooks and release the animal for purposes of chase or safety. 



JExtrinsic Muscles of the Antenna. — At least four take origin near the top of the 

 carapace, two extensors, and two flexors, both sets inclining backwards. A fifth muscle 

 springs from the free entosternite. The innervation of tliis limb is from the circum- 

 03sophageal cord, a point discussed below. 



III. Mandible (PI. I. figs. 4, 4«; PL III. fig. G). — Inserted by a squarish base, 

 having the form of an oblong block, excavated, as it were, on the posterior ventral 

 side to form a long falciform process, the shaft, flattened from before backwards ; at its 

 end it expands into a cutting-blade divided into strong teeth, and bearing at its dorsal 

 edge a short blunt hair bearing a unilateral (ventral) fringe of fine short setae, and 

 presumably tactile or gustatory. Palp a short knob on the antero-ventral side of the 

 basal block, bearing a fine hair, two long plumes as long as the carapace, turned back, 

 and usually lying in the subpleural space. 



The shafts, which are underlain by the paragnathaB of their respective sides, curve not 

 only forwards but upwards, so that the two overlapping and interlocking blades lie 

 actually in the gullet ; and even in extreme abduction they never leave the oral cavity. 



Correlated with the rudimentary palp and want of joints, the mandible lacks com- 

 pletely all proper muscles except a single slip running to the palp. 



Extrinsic Muscles of Mandible. — Long adductor from near top of carapace to inner 

 edge of base, with an external slip continued to the palp. 



Short adductor from side of carapace to same insertion as long adductor. 



Long abductor originating in front of the long adductor, and passing in front of short 

 abductors to be inserted on outer edge of base. 



Short abductors, two strong muscles from free entosternite, inserted on outer side of 

 base, just distal to long abductor. 



IV. Maxilla of the first pair or Maxilla proper (PL I. figs. 5, 5 a). — A two-jointed 

 limb, with a rudimentary biramous palp on the lower joint. 



Basal joint ovoid, slightly sigmoid, flattened above downwards at its distal end; ob- 

 liquely truncated on its inner side for the insertion of the distal joint. 



Distal joint triangular, with the apex forwards and inwards, compressed from above 

 downwards, outer edge convex, prolonged at apex into a strong falciform tooth, just 

 below which is a fine plumose hair. Inner border coarsely toothed, some of the teeth 



