branch divides into two branches that curve to the ventral surface. 

 The more anterior of the branches ends beside the coimnon genital 

 duct. The most posterior surrounds the anus and ends a short dis- 

 tance anterior of this structure. Irregularities in diverticula 

 arrangement are sometimes seen. The median lateral diverticulum 

 may be large and give rise to the anterior of the two ventral 

 branches. 



The various sulci and prominences on the surface of Ornithodoros 

 have relation to these alimentary diverticula. On the dorsum, the 

 transverse sulcus limits posteriorly the central alimentary sac, 

 Ventrally the region between the coxae supports upon its inner sur- 

 face, with which the viscus is in actual contact, the caecal ends 

 of the posterior lateral diverticula. The lesser prominences cor- 

 respond in nearly every case with a particxilar diverticulum and 

 the sulci with the intervals between two diverticula. 



Structure of the alimentary sac. The structure of the sac 

 and its diverticula is identical. The cavity is lined by a single 

 layer of large cells resting upon a thin basement membrane. Ex- 

 ternally, very large single muscular fibres, arranged circularly 

 and longitudinally, form an open meshwork with square meshes as 

 in the mosquito. The lining epithelial cells are large with 

 reticular protoplasm and large vesicular nuclei, some of which 

 project freely into the Ivtmen. Such cells are especially large 

 and have their inner portions much swollen and vacioolated; they 

 may contain dense black globiiles as well as red cells in various 

 stages of intracellular digestion. In addition to large pro- 

 jecting cells, smaller cells, whose nuclei are situated nearer 

 to the basement membrane, are present. Practically all cells 

 of the sac contain small black granules, evidently derived from 

 the digestion of the blood in the lumen. In undistended diver- 

 ticula, the epithelium may form a more or less continuous lining 

 of the tube, but in the distended tube the cells become very un- 

 evenly distributed, being almost absent in some places and in 

 others forming very striking projecting masses. 



Rectum and malpighian tubules . The rectum, which lies im- 

 mediately behind the spermatheca, or the white gland in the male, 

 is an irregular sac having several capacious but short saccular 

 dilatations, (in 0. savignyi ) it receives the rudiment of the 



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