Coxal Organ Morphology and Fiinction* 



Inasmuch as the volume of the blood meal is from two to six 

 times the tick's original body weight and engorgement is usually 

 completed in about half an hour, the tick must have a means of 

 reducing the total intake volume and of preserving the internal 

 medium while feeding. For this purpose coxal organs function 

 as ionic (chloride) regulators and for ultrarapid excretion of 

 a large volume of water during ingestion of blood. Coxal dis- 

 charge, which commences about fifteen minutes after the tick has 

 begun to feed, continues till completion of the meal and inter- 

 mittently for about an hour afterwards. (See also Lavoipierre 

 and Riek 1955). 



Malpighian tubules do not function until about an hovir after 

 feeding is completed, and the amount of water they excrete is 

 limited. 



Chloride regulation . About half the ingested water is ex- 

 creted in coxal fluid. The mean haeraolymph chloride concentration 

 before feeding is l.OC^ and after feeding 0.9^ NaCl; that of 

 coxal fluid is 0.8Q& NaCl. These values are similar to those 

 determined by Bone' (19^3). 



Morphology of coxal organs . The flaskshaped coxal organs, 

 which elaborate Tlie bulk of fluid, consist of an outer filtration 

 chamber with an inner tubule system leading to the external open- 

 ing and of a small organ with glandular structure, the so-called 

 accessory gland. The filtration chamber, which communicates with 

 the tubules of only one point, is highly folded into an elaborate 

 series of pockets and fingers that closely invest the tubules; 



*sChiefly from Lees (19/^^68). See other remarks in section on life 

 cycle. It sho\ild also be mentioned, for practical significance in 

 relation to disease, that Lees fovind that 0. delanoei acinus and 0. 

 parkeri have coxal organs differing from those of 0. moubata, and 

 that in these species coxal fluid is liberated only after cessation 

 of ingestion. It should also be noted that what Lees and others 

 have called '"coxal gland'" is rather a coxal organ (Burgdorfer 1951) 

 because it excretes fluid rather than secreting fluid, and the 

 filter chamber histologically has no glandular structvire. 



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