96 BIOLOGICAL LECTURES. 



first view of great complexity, so that they might seem to 

 entirely justify Binet's views as to the height and variety of the 

 psychic powers of these organisms. These activities and their 

 explanation have been discussed somewhat fully by the writer 

 in a paper l devoted entirely to the psychological aspect of the 

 matter, so that only so much of this aspect will be taken up at 

 present as has a necessary relation to the questions proposed. 



If we place a number of Paramecia, in the culture water in 

 which they are found, upon a glass slide, and cover with the 

 cover glass, we soon find that the animals, which were at first 

 scattered uniformly, have gathered into groups in one or more 

 parts of the preparation. Usually we find that a bit of bacte- 

 rial zoogloea forms the center of such a group ; as many of the 

 Paramecia as can do so have pressed their anterior ends against 

 the mass, the ciliary current carrying bacteria to their mouths ; 

 others press in from behind. It is well known, of course, that 

 Paramecia make no choice in the food which the current brings 

 to their mouths, taking in particles of all sorts indiscriminately. 

 The possibility may suggest itself, however, that they have 

 gathered about these masses of zoogloea because the latter 

 serve them as food. The choice of food would thus occur a 

 step sooner the Paramecia choosing their food by gathering 

 about it, then taking whatever comes. But if we introduce into 

 the slide a bit of filter paper or a fine raveling of cloth, we find 

 that the Paramecia gather about it with the same apparent 

 avidity as about the zoogloea, pressing the anterior end against 

 it and remaining thus, quiet, for long periods. 



This and other experiments show, therefore, that this gather- 

 ing about a bit of bacterial zoogloea or other substance is not the 

 expression of a choice of food, but is merely a manifestation 

 of the fact that the Paramecia react to contact with solids of a 

 certain physical texture by suspending active locomotion and 

 remaining against the solid. A similar reaction to solids is, of 

 course, a very common phenomenon among organisms of dif- 

 ferent sorts; it has received the name "Thigmotaxis," or 

 " Stereotropism." 



1 " The Psychology of a Protozoan," Amer. Journ. of Psychology, vol. x, 

 No. 4, 1899. 



