34 



LEECHES 



Mouth 



Auricle 



Anus 



Buccal fri 



2mm 



Fig. 21 . (a) anterior end of Haemadipsa in ventral view to show 

 buccal frill; (b) posterior end of Haemadipsa in dorsal view 



to show auricles. 



contact with the posterior sucker (Fig. 21). The products of the 

 nephridia are used to moisten the suckers, and are conserved by 

 special frills and muscular rims on the suckers themselves. 



5 . Pharyn gobdellae 



The Erpobdellidae, sometimes knov^n as the v^orm-leeches, 

 are freshw^ater or amphibious leeches which have lost the power 

 of penetrating the tissues of a host and sucking blood. The pharynx 

 has muscular ridges homologous with those in the Hirudidae, 

 but no jaws or teeth. These leeches are carnivorous and worms, 

 insect larvae, etc., are swallowed whole. The gut is simple and 

 without diverticula. The plan of the reproductive system is fairly 

 typical, except that the testes are concentrated in the posterior 

 one third of the body and are very abundant. Erpohdella octoculata 

 is common in freshwater habitats of Europe and Asia, and is truly 

 aquatic. In North America the corresponding leech is Erpohdella 

 punctata. Erpohdella has five annuli per segment, but other mem- 

 bers of the family have one or more of these annuli subdivided. 

 Thus Dina, which is represented in both the Old and New Worlds 

 has the last annulus of each segment divided into two. This 

 tendency is carried furthest in Trocheta where the typical condition 

 is three wide and five narrow annuli per segment, but further sub- 

 division may lead to eleven annuli per segment. Trocheta spends a 



