146 



LEECHES 



Table 10. Comparison of the Life Histories of 

 Glossiphonia complanata and Erpohdella octoculata 



forms greatly outnumber the sanguivorous parasites and these 

 tend to feed on a wider variety of animals, so that almost any 

 aquatic habitat will contain some suitable food organisms. For 

 these the chemical and physical characters of the environment 

 sway the balance in their competition with other organisms, the 

 oxygen and calcium content of the water and the rate of water 

 movement being particularly important. 



