numerous small muscle fibres inserted in these pockets pass out- 

 wards from the orgsin to attachments on the body wall. The histol- 

 ogy of the two regions is entirely different. The filtration 

 membrane is only one or two microns thick and its cellular origin 

 is much obscured. The tubule walls, from five to thirty microns 

 thick, are composed of cells with a dense, deeply-staining cyto- 

 plasm and are richly supplied with tracheae. 



Function, The production of coxal fluid is under muscvilar 

 control. It is believed that contraction of coxal organ muscles 

 enlarges the filtration chamber and sets up a sufficient pressure 

 difference across the membrane to initiate filtration into the 

 organ. In subsequent passage of fluid down the tubules, threshold 

 substances such as chloride are reabsorbed. That the coxal fluid 

 is primarily an ultrafiltrate of the haemolymph is sioggested by 

 (a) the rapid passage of dyes and even haemoglobin into coxal fluid 

 after injection into the haemolymph, and (b) the very high rate of 

 fluid liberation. Serum albumin sometimes passes into coxal fluid 

 after injection, but casein (and normal haemolymph proteins) are 

 fully retained (Lees' summary). 



Bon^ (1943) proposed somewhat different explanations concerning 

 coxal organ function. Lees further indicates that Patton and Evans' 

 (1929) opinions regarding the functions of the coxal organs are in- 

 correct. An earlier work on the same subject is that of von 

 K'linssberg (1911 ). 



The small accessory coxal glands have an unknown function. 

 Rapid engorgement in argasid ticks is allowed by passive cuticular 

 stretching. In ixodid ticks new cuticle is produced to allow for 

 volume of intake ajid engorgement is much more slowly accomplished. 



When specimens of 0, moubata and other argasid ticks that 

 possess coxal organs are warmed or irritated they extide from these 

 organs a clear fluid. This may possibly serve in part as a defen- 

 sive mechanism althoiigh the actual reason remains to be determined, 

 Coxal organ discharge has been observed and reported, highly in- 

 accurately, by Remy (1922A, and for Argas reflexus, 1921 and 1922B), 

 who believed the exudate to be haemolymph containing haemocytes. 

 Lees (19A-6B) has shown that these structures axe actually small, 

 globular clusters of refractive granules, possibly derived from 



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