78 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



manner, thus A- The cuticle covering each of them is thick- 

 ened along its margin into a large number of sharp calcified 

 teeth. The remainder of the fore-gut is constituted by an ovoid 

 muscular pharynx, with which the buccal cavity communicates 

 by an extremely small aperture. Its wall is thick, and numerous 

 dilator muscles radiate from it to the body-wall. The pharynx 

 is surrounded by a large number of salivary glands, each of which 

 is a large cell from which a slender duct runs forwards to open 

 on one of the jaws. 



The mid-gut (mesenteron) commences with a short and narrow 

 gullet (oesophagus) leading from the pharynx to a very large crop 

 which constitutes the greater part of the gut. The crop is a 

 thin- walled tube which gives off 11 pairs of lateral pouches, 

 corresponding but not limited to segments 4-14, and increasing 

 in size from before backwards. The last pair are much the 

 largest, and extend backwards by the sides of the intestine. A 

 small rounded stomach terminates the mid-gut. 



The hind-gut (proctodseum) consists of a narrow tube, the 

 rectum or intestine, running from the stomach to the anus. A 

 spiral fold projects into its interior. 



The food consists of blood sucked from a higher animal, attach- 

 ment being effected by the anterior sucker, and a three-ra} r ed cut 

 made by a sawing action of the jaws. Meanwhile a fluid is 

 poured out from the salivary gland by which the blood of the 

 victim is prevented from coagulating. The pharynx acts as a 

 suction-pump, its cavity being alternately enlarged by contraction 

 of the dilator muscles and diminished by contraction of its 

 muscular wall. A very large amount of blood can be sucked 

 at one time, and this is stored up in the capacious crop. Meals 

 are often infrequent and they take a corresponding time to digest, 

 even as much as nine months. This is accounted for by the fact 

 that digestion and absorption take place only in the relatively 

 small stomach. 



4, The Circulatory Organs consist of a blood-system which 

 freely communicates with a reduced coslomic system, both alike 

 containing blood coloured red by haemoglobin. There are numer- 

 ous colourless corpuscles. 



The blood-vessels are distinguished from the ccelomic spaces 

 by the possession of definite muscular walls lined by epithelium. 

 A large lateral vessel runs along each side and is connected with 



