to 
NI 
N 
GA Pal Re XX XX 
THE ZOONITES. 
THE study of the annelids, which has been pursued with great zest 
since the beginning of this century, has been productive of eminent 
service both to anatomy and to comparative physiology. These 
animals, composed of rings placed side by side and each containing 
the same organisation, present a very curious structure. The 
THE DRAGON-LEECH. 
(Hirudo troctina.) 
common leech (Hzrudo medicinalis) may be considered typical. 
As every one knows, its shape is like that of a short, thick worm 
or garden slug, its body attenuates towards each extremity, where 
it terminates in a sucker; the one is the ova/, and the other the 
anal. This body is composed of ninety-five rings. On close 
observation, its back is seen to be marked with triangular brown 
spots; these are arranged in rows parallel to the rings, and are 
repeated every five rings. In the dragon-leech, which is here 
