HIRUDINEA 133 
was the space in which the inner ends of the nephridia lay, 
and was archicoelic in its origin. In Hirudinea this space is 
divided into two: a series of spaces lined with an endothelium, 
the true vascular system ; and a series of sinuses with no special 
Fic. 84.—Diagrams of transverse 
sections: I., through Clepsine ; 
II., through Hirudo. A. G. 
Bourne. 
a 
Alimentary canal. 
Dorsal sinus. 
Nerve cord. 
Ventral sinus. 
Lateral sinus. 
6. Ovary. 
7. Dorsal blood-vessel. 
8. Inner end of nephridium, 
9. Testis. 
0 
1 
) 
oUe cot 
. 
. Lateral blood-vessel. 
. Nephridium. 
12. Vesicle of nephridium. 
cellular lining, and enclosing various organs of the body, the 
coelom. These two series of spaces open into one another 
directly in the Rhynchobdellidae, and through the botryoidal 
tissue in the Gnathobdellidae. In Clepsine (Fig. 84, I.) and 
Pontobdella the dorsal sinus contains a dorsal vessel, the ventral 
sinus contains the nervous system, a ventral vessel, the ovaries, 
and in Clepsine the inner ends of the nephridia. There are 
also two lateral sinuses in which in Pontobdella a lateral vessel is 
found. In Hirudo (Fig. 84, IL.) there are a dorsal and ventral 
sinus, and two lateral vessels. The ventral sinus encloses the 
nervous system. The ovaries and testes lie in special sinuses. 
The internal end of the nephridium is placed in the testis sinus 
in those segments in which both occur. 
The alimentary canal of Leeches falls into five sections: 
G.) the muscular pharynx, which may possess two or more 
commonly three jaws, and numerous glands whose secretion in 
Hirudo serves to prevent the blood upon which the animal 
lives from coagulating; (ii.) the oesophagus and proventri- 
