50 



The Structure and Arrangement of the Mouth Parts and 

 Alimentary Canal of Ornithodorus Moubata. 



The general arrangement of the mouth will be seen from 

 the diagram. (Fig. 18.) The boring instrument or rostrum 

 consists of three parts, two chelicerse (oh.) and a ventral 

 hypostome (H.). The cheliceraa are hollow chitinous organs, 

 inside which are muscles which operate the terminal claws ; 

 the hypostome is barbed. In the act of boring the claws are 

 straightened and the three parts of which the rostrum is 

 composed are advanced a little further. The claws are 

 again advanced for a further pull, and the barbed hypostome 

 prevents any slipping back. By a succession of these efforts 

 the rostrum is buried in the skin. 



FIG. 19. 



Diagram of alimentary canal and mouth parts of tick (Orni- 

 thodoros moubata). PP, Pedipalps. K, Eostrum. SD, 

 Salivary duct. SG, Salivary gland. ST, Stomach. I, In- 

 testine. CL, Cloaca. MT, Malpighian tube. 



The three instruments of the rostrum, when apposed, form 

 a canal at the base of which is the mouth. This widens 

 into a pharynx, which is alternately compressed and 

 expanded by a coordinated contraction of the individual 

 muscle fibres attached to it. The blood is driven by the 

 pump through the narrow oesophagus into the crop or 

 stomach (Fig. 19) (st.). The stomach is a capacious pouch 

 having extensive lateral diverticula, which themselves branch 

 so that after a full meal the organ distends the insect. The 

 intestine is a very narrow tube connecting the stomach to 

 the cloaca (<?.). The anus is not terminal, but opens in the 

 mid-line just behind the last pair of legs. The salivary 

 glands (s.ff.) are of the compound racemose type, each with 

 one duct (s.d.) passing forward to the mouth. 



Koch was of opinion that the spirochsetse passed from 

 the salivary glands during the act of sucking, but both 



