307 



On examining fig. 2 , it will be noticed , that a dark line goiug 

 from the central bundie towards the side of the jaw , is drawn 

 here and there, 



This line is nothing but a glandduct leaving the central 

 bundie and opening on the side of the jaw; the duet is filled 

 with granules and gets frora them its dark colour. 



This duet may be called a vas aberrans. I will come back to 

 this point later on. 



The teeth or denticules are composed of carbouide of linie ex- 

 cept in the genus Leptostoma '), here being chitinous. 



In order to study the shape of the teeth I have isolated them 

 by placiug the jaw for some time in a solutiou of caustic po- 

 tass. The teeth of the Hirudinea are generally conical and the 

 biggest, situated in the middle are provided with two roots, see 

 fig. 5. 6 and 7. The surface is generally rather smooth, the teeth 

 of Aulastomum gulo show some little tubercles on their surface, 

 but the geueral form of the teeth diiïers very little from that of 

 the other Hirudinea. 



The size of the teeth is very different. The largest are found 

 in Aulastomum gulo, while those of Limnatis africana belong to 

 the smallest; the latter do not surpass V^o mM. in greatest dia- 

 meter. This is remarkable as Limnatis nilotica has jaws , which 

 are constructed quite in the same way as Hirudo, but misses 

 the denticules. Moquin Tandon and Savigny say that Limnatis 

 nilotica has no teeth , while Peters contradicts it. It is possi- 

 ble, I think, that the individuals of Limnatis nilotica diverge 

 on this point from each other, especially because another species 

 of the same genus (Limnatis africana) possesses very small teeth. 



The number of denticules can vary from 8 to 130. Hirudo 

 africana^) has 115 — 130 teeth. Hirudo medicinalis 90 — 100. Hi- 

 rudo decora ^) from Minnesota 55. Haemopis vorax 30. Macrob- 



1) Whitman. Leeches of Japan. Quart. Journ. mier. Sc. vol. 26 p. 317. 



2) Whitman 1. c. 



3j Verrii. Synopsis of the North American Fresh water Leeches. Rep. U. S. Com. 

 Fish and Fisheries. 1871 — 1873. Washington. 



