284 GENERAL BIOLOGY 



This is readily understandable when it is realized that the leech 

 has three chitinous jaws to form the mouth (which lies within the an- 

 terior sucker). These jaws bite into a region, and a secretion from the 

 mouth-glands is poured out which prevents the host's blood from coagu- 

 lating. It is thus difficult to stop the bleeding after the animal has 

 moved to a new location. 



The digestive tract of the leech is especially adapted to the diges- 

 tion of blood of vertebrates, upon which the leech feeds. There is a 

 muscular pharynx and a short oesophagus leading to the crop. This 

 crop has eleven branches or diverticulae. Then there is a stomach, an 

 intestine and an anus. The leech can ingest about three times its own 

 weight of blood. 



There is a peculiar kind of connective tissue known as botryoidal 

 ( ) tissue which develops in what should be the 



coelom. This body-cavity is therefore very small, although there are 

 spaces in the coelom which are not filled with this tissue, these spaces 

 being called sinuses. 



There are seventeen pairs of nephridia, quite like those of the earth- 

 worm (except that they sometimes do not have an internal opening) 

 which carry waste products from the coelomic fluid and from the blood. 

 Respiration takes place at the surface of the body through the many 

 blood-capillaries found in the skin. 



There are nine pairs of segmentally arranged testes which empty 

 their sperm into the vas deferens, then into a much-folded tubule called 

 the epididymis. Here they are fastened into bundles known as sper- 

 matophores. They are then ready to fertilize the eggs of another leech, 

 after passing out of the copulatory organ. 



The eggs develop in a single pair of ovaries, from which they pass 

 through the oviducts into the uterus, and finally out through the genital 

 pore situated on the ventral side of the ninth segment. A cocoon is 

 formed after copulation quite like that in earthworms. 



