THE LEECHES (HIRUDINEA) 647 



developed and the neural annulus is usually less divided than the 

 others. 



Setae are always absent, except in Acanthobdella, and suckers 

 always present, except in a few exotic, chiefly burrowing, genera. 

 The oral sucker surrounds the mouth, sometimes forming mere 

 lips and being widely expanded only in Ichthyobdellidae and a few 

 Glossiphonidae. The caudal or subanal sucker is larger, discoid or, 

 more rarely, deeply cupped, and widely expanded beyond its con- 

 stricted central pedicle. There is a powerful and elaborate muscu- 

 lar system, consisting of circular, oblique, and thick, longitudinal 

 coats, as well as vertical and radial sheets and fibers. 



The digestive tract is divided into buccal chamber, pharynx, 

 esophagus, stomach or crop, intestine and rectum. In the jawed 

 leeches the mouth is large; in the proboscis leeches a mere pore in 

 the disk of the sucker. In the former the buccal chamber usually 

 contains three compressed muscular jaws bearing serial teeth on 

 the ridge. The pharynx is a muscular bulb, a straight tube, or a 

 slender, exertile proboscis moving within a sheath. Salivary glands 

 may open into the short esophagus or on the jaws. The large 

 stomach or crop varies with the nature of the food and may be a 

 straight tube, or complicated by from one to twenty pairs of simple 

 or branched lateral ceca, of which the posterior pair is largest and 

 most constant. Generally short and simple, the intestine may 

 bear four pairs of simple ceca (Glossiphonidae). A short, narrow 

 rectum opens by a small dorsal anus usually behind XXVI or 

 XXVII, but rarely behind XXIII. 



Leeches are hermaphroditic. The genital orifices are median, with 

 the male pore preceding the female. The testes (really coelomic 

 sacs enclosing the testes) vary from one elongated pair in Acan- 

 thobdella to usually six (five to nine) pairs in the Rhynchobdellae, 

 nine or ten (five to nineteen) pairs in the Hirudinidae, and very 

 numerous small ones in the Herpobdellidae. A vas deferens on 

 each side continues into an epididymis and an ejaculatory duct 

 which may be provided with a sperm sac and a glandular region 

 for forming the horny spermatophores. The two ejaculatory ducts 

 open into an unpaired genital bursa or a more complex atrium 

 which may be elongated into a highly muscular sheath enclosing a 



