B48 STUDIES IN GENERAL PHYSIOLOGY 
its possession of two tentacles (Fig. 98). From the posterior 
side of the brain arise the two large nerves (n, Fig. 98), 
which traverse the entire length of the animal. A number 
of other nerves also run to the brain. The nerves contain 
separate ganglion cells, a characteristic which, as is well 
known, is found also in certain peripheral nerves in the 
higher animals. The nerves forma plexus at the periphery.’ 
The central nervous system of this animal therefore con- 
sists mainly of the ganglion situated at the anterior extremity 
of the animal. As is the case with all Planarians, Thysano- 
zoon creeps over the walls of the aquarium or along the 
surface of the water. It differs in its movements from the 
fresh-water Planarians only in so far as it is able to execute 
actual swimming movements. In swimming the animal 
executes pendulum-like movements with the lateral portions 
of its body as does a butterfly with its wings. 
If a Thysanozoon is cut across transversely into two 
halves, while the animal is moving at the surface of the 
water, the posterior aboral half at once falls to the bottom 
like a dead mass, while the oral piece which contains the 
brain continues to move along quietly. If the cut is made 
rapidly and with a sharp pair of scissors, the behavior of 
the oral piece gives no indications of such reactions as 
accompany the sensation of pain in higher animals. If the 
animal is divided with a sharp knife while it is creeping over 
a glass plate, we notice the same phenomenon: the oral 
piece continues its motion undisturbed while the progressive 
movements of the posterior piece cease at once. It happens 
occasionally that the transverse division of a Thysanozoon 
causes the oral piece to execute more lively and rapid move- 
ments. That the progressive movements of this animal are 
indeed a function of the brain is shown particularly well 
when only the exceedingly small piece which contains the 
1 Mittheilungen aus der zoologischen Station zu Neapel, Vol. I. 
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