KEVIEW OF GENUS ARGULUS — MEEHEAN 463 



On the ventral side the various appendages can be seen (fig. 21, a). 

 On the anterior end of the body are two pairs of antennae. The 

 first segment of the anterior pair is chitinized, sometimes with a 

 spine at the base. The second segment is enlarged and prolonged 

 into a lateral hook. On the anterior surface of the hook there may 

 be a fingerlike prolongation with or without another anterior hook. 

 In a few instances this may be a mere knob or almost missing. Often 

 there is also a ventral spine on the posterior surface of the hook 

 mesial to the base of the flagellum which extends to about the length 

 of the lateral hook (fig. 21, c). 



On the second antennae the proximal segments are enlarged, usu- 

 ally with a spine at the base. The distal segments are slenderer 

 and considerably longer than those of the first antennae. Near the 

 midline of the body just posterior to the antennae is another pair 

 of spines, the postantennal spines. All these spines will be used in 

 identification. 



According to Martin (1932) the spine sometimes seen on the in- 

 terior of the lateral hook will become the exoskeleton after ecdysis. 

 The end of the hook is perforated with a gradually widening canal 

 leading back to a chitin-lined sac thrown into many folds with a large 

 number of chitinous hairs. It is probably gustatory in function. 



In the longitudinal groove running forward mesially between the 

 antennae is a preoral sting, which is retractile into a sheath and at the 

 base of which is a poison gland. Posterior to this sting is the 

 proboscis, which also lies in the groove when at rest but which is 

 erected at right angles to the body when functioning. It is a 

 cylindrical bulbous structure somewhat larger in size than the sting 

 and carries the true mouth. The framework is of chitinous bars, 

 which enclose the buccal cavity and extend into the proboscis. 



The buccal cavity is formed by the delicate upper lip and the more 

 bulbous lower lip. The anterior portion of the buccal cavity contains 

 a pair of swellings ending in hollow spines, the labial spines. They 

 come in contact with the host first. Martin has shown that very 

 early in embryonic life these develop from the lower lip. 



The mandibles project from the sides and are completely enclosed by 

 the buccal cavity when at rest. The basal segments of the mandibles 

 assist in the formation of the proboscis in a very early embryonic 

 stage by fusion of the distal portions of the basal segments with the 

 lips. In this way the upper and lower lips form the dorsal and 

 ventral walls, and the mandibles the lateral walls, of the buccal 

 cavity. 



The suction cups, or so-called sucking disks, develop from the 

 maxillae on each side of the preoral sting. They have a flat rim 

 covered by a chitinous exoskeleton with thickenings like ribs radiating 



