150 
$ 6. Thigmotactical phenomena. 
Under special circumstances Chlamydomonas variabilis 
Dangeard has a strong inclination to attach itself to the 
glass wall with the cilia. (See fig. 1. A). This phenomenon 
is seen with many unicellular organisms. An easy object, 
to learn a little more about it, we find in Paramaecium 
(Jennings 1914, page 87). The sticking takes place with 
this Protozoën at the close of a number of changes of 
movement. The animal swims up against a firm object, 
makes the motor-reflex movement, now swims up against 
it with a diminished rapidity and stops its motion against 
the object, while it sticks to it with some cilia. The whole 
phenomenon is sometimes called thigmotaxis. With Chla- 
mydomonas, Ï was able to observe, of the whole number 
of phenomena, only that the Alga attached itself. Probably 
this takes place at the ends of the cilia. After the attaching 
the motility needs not to stop. With individuals, that still 
move, after they are attached, we can observe, that the 
space in which the body moves, is much greater than the 
volume of it, from which we may. conclude, that the 
object is not attached with any part of the surface of 
the body, but with one or with both the cilia. The 
movement to and fro, which can be made yet, proves, 
that the cilia still move. It is probable that the attaching 
takes place at the ends of the cilia. 
In this attaching [I think to see a pure physico-chemical 
process. Small particles of dead matter can also stick to 
the wall of the vessel under some circumstances. Perrin 
(1914. page 139) made use of this, to count the number 
in a suspension of particles of catgum. To this purpose 
he added to the water a small quantity of acid. Every 
particle, that was driven against the side by the Brown 
movement, stuck there. In colloïd chemistry too the 
phenomenon of sticking is known; there the term “sticking- 
