122 BEHAVIOR OF THE LOWER ORGANISMS 



p. 388). But it is notable that in none of these cases has the relation 

 of the direction of turning to the differentiations of the body been ob- 

 served, and this is the crucial point for determining the nature of the 

 reactions. The fact that it is only for these very difficult objects that 

 the direct turning is maintained must make us cautious in accepting 

 this exceptional result. 1 



Let us now leave the method of reacting, and turn to certain more 

 general phenomena. In what chemicals do infusoria gather? What 

 chemicals do they avoid ? 



In no other infusoria is the behavior toward different chemicals so 

 well known as in Paramecium. Chilomonas collects in acids in gen- 

 eral, and especially in solutions of carbon dioxide, just as Paramecium 

 does. Spontaneous gatherings are often formed by Chilomonas, and it 

 seems probable that these are due, as in Paramecium, to the carbon 

 dioxide produced by the animals themselves (Jennings and Moore, 

 1902). Cyclidium glaucoma and Colpidium colpoda likewise collect in 

 carbonic and other acids. Opalina, Nyctotherus, and Balantidium en- 

 tozoon, living in an alkaline medium, gather in acids, but if transferred 

 to an acid medium, they gather in alkali (Dale, 1901). Many other in- 

 fusoria show no tendency to gather in acids. Loxocephalus granulosus 

 and Oxytricha ceruginosa form spontaneous collections resembling pre- 

 cisely those of Paramecium, but they are not due to the same cause. 

 These species do not collect in solutions of carbon dioxide, nor in other 

 acids. When they are mingled with Paramecia in the same prepara- 

 tion, they collect in one region, while the Paramecia collect in another. 

 It is apparent that Loxocephalus and Oxytricha produce some substance 

 to which the collections are due, and that this substance is not carbon 

 dioxide. A number of other infusoria form spontaneous collections, 

 the cause of which has not been investigated. Many of the commonest 

 species do not form such collections. 



There are many chemicals in which one or another species of infusoria 

 have been found to collect. Most of the details are of comparatively 

 little general interest from the standpoint of animal behavior, so that we 

 shall not take them up here. An excellent summary of these results will 

 be found in Davenport's " Experimental Morphology " (Vol. I, pp. 32-45). 

 Certain general features are important for our purposes; these we may 

 bring out briefly. 



First, from the way the collections are brought about, it is evident 

 that whether given infusoria tend to collect in a certain solution or not 

 depends on the nature of the solution in which they are already found. 

 This has been illustrated in detail for Paramecium. Paramecia in 



1 For a discussion of related points, see Chapter XIV. 



