intestine and the two malpighian tubules (but in 0. rooubata the 

 rectum receives only the malpighian tubules and tTiere is no con- 

 nection between intestine and rectal ampulla). Its walls are 

 extremely thJin and consist of a single layer of flattened cells. 

 It contains a white fluid identical with the secretion of mal- 

 pighian tubules. The rectum therefore does not serve as an ad- 

 junct to the alimentary canal, but fiinctions as an excretory 

 receptable. The white matter passed ^er anum by ticks also can- 

 not, strictly speaking, be regarded aTTeces. 



The malpighian tubules are important because of their great 

 length and functional activity ajid because of the frequency with 

 which such organs are utilized by parasites in other animals. 

 They consist of two long, fine white or transparent tubules 

 arising on either side from the rectum, and after a complicated 

 course anxjng the viscera, ending blindly in the anterior portion 

 of the body. These tubules come in relation with almost every 

 important organ in the body and drain every quarter of the body 

 cavity. The tubes in young ticks are of an even calibre through- 

 out and contain small quantities of secr-tion only. They are 

 often swollen in aged ticks to form sacs similar to, but smaller 

 than, the rectum. After oviposition the tubes and rectum may be 

 greatly distended with characteristic white fluid that is evident 

 externally as patches of lighter color. It is probable that the 

 appearance is that described as a '"fungus"' in these ticks by Well- 

 man (1906A,D,1907B). 



Feeding habits of 0. moubata have been discussed in the sec- 

 tion on the life cycle of this tick. Certain aspects of digestion 

 and excretion of fluids are of considerable practical importance 

 for they concern, at least, the fate of ingested spirochete para- 

 sites of relapsing fever (Borrelia spp. ) and the discharge of_ 

 these organisms onto or into a new vertebrate host when the tick 

 subsequently feeds. 



Digestion 



The volume of a blood meal is from two to six times the tick's 

 original body weight (Lees 1%6b). During ingestion, the cuticle 

 stretches to accomodate this huge amount of fluid. Engorgement is 

 completed in about half an hour. In order to reduce this tremendous 

 volume ingested so rapidly, fluid is discharged from the coxal or- 



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