482 Journal of Coinparative Neurology and Psychology. 



animals, and this becomes still more evident when one observes 

 the accidental manner in which the\' are formed, the way in 

 which the individuals are dragged about against their efforts, 

 and their struggles to free themselves — at times resulting suc- 

 cessfully. I have even seen moribund individuals, and individ- 

 uals undergoing fission thus attached irregularly to the oral sur- 

 face of other specimens. 



2. A second important factor in bringing about conjuga- 

 tion is found in the usual ciliary movements of the animals and 

 in the currents produced by these movements. As we have 

 seen in the foregoing pages, there is a strong current passing 

 backward along the oral side of Paramecium, so that there is a 

 tendency for all sorts of objects suspended in the water to be 

 carried to the oral groove. This tendency is of course opera- 

 tive on other Paramecia in the neighborhood as well as upon 

 lifeless objects. In the case of two Paramecia close together 

 this tendency is of course reciprocal ; each tends to draw the 

 other to its own oral groove. Thus if two Paramecia are swim- 

 ming along close together, there is a strong tendency, through 

 their usual n^ovements, for them to come together with oral 

 surfaces in contact. Under ordinary conditions this is often 

 seen, but does not lead to conjugation, because the oral sur- 

 faces are not adhesive. But when the oral surfaces are adhe- 

 sive, as we know them to be at periods of conjugation, then 

 the animals stick together. The remainder of the process falls 

 outside the field of "behavior." The relations just pointed out 

 show why in a conjugating culture so many more individuals 

 are found in contact by their oral surfaces than in the irregular 

 ways shown in Fig. 1 3 ; the irregular adhesions occur only 

 through unusual accidents. 



Thus when the oral surfaces of Paramecia become adhesive, 

 the usual movements lead to attachment by these surfaces, such 

 as we find in conjugation. All the phenomena seem to be in- 

 telligible on the basis 01 these factors alone, though it may be 

 possible that there are certain modifications of the usual be- 

 havior in periods of conjugation. 



