26 THE ECOLOGY OF ANIMALS 



animals in aquariums by Boulenger (1929). Keeble 

 (1910) demonstrated the persistence of tidal rhythms 

 of activity in the marine flatworm {Convoluta roscoff- 

 ensis) when brought into the laboratory. The whole 

 question is of great importance in medical ecology. 

 Many malaria- carrying mosquitoes are active only at 

 night or at dusk, while the tsetse flies {Glossina), 

 which carry the trypanosome of sleeping sickness in 

 Africa, are active during the day. There is one 

 species of pathogenic Filaria (a roundworm) whose 

 larvae abound in the peripheral blood- circulation of 

 infected human beings during the day and are spread 

 by the bite of a diurnal fly, while another species 

 appears in the outer blood at night and is spread 

 by a mosquito. Similarly, the itch-mite of scabies 

 {Sarcoptes scabiei) becomes active under the skin at 

 night, causing intense irritation. 



It is important, then, to reaUze that most com- 

 munities are of a dual nature, having two different 

 sets of animals working as it were in shifts, and 

 coming into activity alternately. The next step is 

 to classify animals by their food-habits. Animals 

 differ biologically from plants in the variety of their 

 food-habits, and the fact that they prey to a large 

 extent on other animals and on plants. It is these 

 facts that make the methods of animal ecology totally 

 different from those of plant ecology. The botanist 

 determines the available food of plants by studying 

 the soil and the sunlight. The animal ecologist has 

 to study the plants themselves and most of the 

 animals as sources of the food of animals. The first 

 type of work can be done by physical and chemical 

 methods. The second involves an enormous amount 

 of natural history observation and experiment, and 

 at the same time makes the study extremely fascinat- 

 ing owing to the number of curious adaptations and 

 habits that are met with. In seeking to understand 

 the general organization of animal communities the 

 student will have to resist the inclination to follow 



