818 



OKESSWKI.I, SHKAliEK. 



than these last. The cubical basal pieces with which it 

 articulates support four arms on each side, each being com- 

 posed of three or four pieces, the last of which is fashioned 

 into a sharply-curved claw-like tooth. This is strongly 

 serrated on its inner edge. One difference between the jaw 

 parts of Histriobdella and Stratiodrilus consists in the 

 length of the middle joint of these arms. They are much 



Text-fig. .">. 



■m.d.i 



bl. 



f — 



m 



-■^;^^ 



-' b^p j- 



sb.m j. 



Jaw apparatus. Enlarged figure showing the sti'uctnre of 

 tlie teeth and the arrangement of tlie jaw-muscles, ha.p.j.. 

 basal piece of jaAvs ; hi. m., Jmlh-like muscular organ of the 

 jaws; /.. fulcrum; vi.d.j.. strands of the dorsal longi- 

 tudinal muscle-bands running to the jaws; st.vi.j., 

 striated muscles of the jaws : //(.. teeth. 



longer in Histriobdella, and allow of the teeth being 

 folded back in the mouth or oesophagus to a greater extent 

 than in Stratiodrilus. When at rest in the ordinary 

 position the teeth are not folded back to their full extent. 

 The middle piece of the arm projects at right angles to the 

 jaws, and in this position the most anterior part of the arm is 

 the distal joint, the tooth being strongly flexed. When the 



