TYPICAL SEGMENTS OF HIRUDO. 



fraction shows the proportion of the length of the ganglion lying 

 within it ; while a figure like 1.5 shows that the posterior part of 

 the ganglion lies 0.5 of its total length in front of the limit be- 

 tween the sensory ring and the fifth ring of the preceding somite. 

 By means of the sections the position of the ganglia and the 

 prominent constriction of the alimentary tract ( C) was in each case 

 determined. For the position of the other organs, I relied upon 

 a study of the gross dissections. 



-v.d. 



Segments of XV, XVI and XVII of Hirndo medicinalis (X I2 )- 

 The outline of the alimentary tract is shown by the heavy line on the right side of 

 the plate. Structures underlying other organs are shown by broken lines. Organs 

 or parts of organs lying beneath portions shown by broken lines, are represented by 

 dotted lines. 



n, nephridium ; np, nephropore ; /, testis ; g, ganglion ; c, constriction of ali- 

 mentary tract ; nv, nephridia.1 vesicle ; I'd, vas deferens ; h>, lateral vessel. 



The results can be best studied by referring to the accom- 

 panying plate. In the region presented by it, the alimentary 

 tract consists of a rather narrow tube with two pairs of out- 



