THE ZOONITES. 281 
arises ; therefore, we may well consider the planaria no exception 
to the zoonite theory. 
Some years ago, a great number of physiological facts were 
brought to light, which seem to show that the leech had not only 
a general life—an associate life, if we may use the word—but also 
an zzdtvidual life, each of the zoonites (or associated parts) having 
its own life. For the sake of general harmony, Nature has provided 
the annelid with nerves of communication, which join the separate 
organs to each other. The chief zoonite is the one whose nerval 
centre is the best developed, and which carries the most organs 
of sense. This may be considered the governor of the association 
—the pilot of the vessel. If this be destroyed, the others continue 
to live, but without order or regularity ; the animal is no longer 
able to provide for its nourishment or its necessities. The sub- 
joined experiments evidently show that the lives of the zoonites 
are, in a certain sense, independent of each other. 
1. If the first zoonites of a leech full of blood be wetted 
with salt water or weak acid, the stomachs corresponding to them 
will disgorge their contents, but the rest will retain the blood. 
2. If you partially immerse a leech in concentrated alcohol, that 
part is alone deprived of its vitality. 3. If you cut a leech in two 
which is three parts full of blood, and still attached to the skin, it 
will continue to suck while the blood flows from the wound. 4. If 
by any means a zoonite be kiiled near the centre of the animal, the 
anterior and posterior parts will still live, two leeches being produced 
by the division of one. 5. If you cut on each side of a ganglion 
the nerves which unite it to its neighbours, you will produce an 
isolated zoonite between two multiple animals. By pricking the 
various parts this isolation of sensation will be apparent. 6. If the 
medullary canal, the great nerve which connects the ganglions, be 
severed in any part of the leech, the two parts of the animal will 
possess different volitions. All the phenomena of sensation and 
locomotion will be perfectly distinct in each part. Dr. Verniére 
experimented upon a leech in this way, and kept the creature for 
two months after the operation. Nothing could be more singular, 
he says, than watching the conflicting wills in the two extremities 
of the same creature. When each sucker was fixed on the walls of 
