282 HIGH SCHOOL ZOOLOGY. 



driven upon the shore. It is believed that the littoral fauna 

 oi'iginated from the pelagic in the first place, while many pel- 

 agic forms, such as the whales, are undoubtedly derived second- 

 arily from shore forms. The origin of fresh-water faunas is 

 another point of great interest ; certain stages through which 

 they must have passed may be seen in the mouths of rivers 

 where different species extend upwards to a greater or less dis- 

 tance, according as they are moi-e or less tolerant of the dimin- 

 ished salinity of the water. That part of the fresh-water 

 animals are so derived may be gathered from such cases where 

 they exhibit little or no difference in their new habitat, (VI, 34, 

 VII, 13). There are many curious facts in the distribution of the 

 fresh-water fishes, which indicate the early separation of some 

 groups from marine forms, and which can only be explained 

 by realizing that changes in the configuration of the land 

 must have involved many changes in the gi-eat water-courses. 



In inland lakes we have also littoral, deep, and pelagic 

 faunas, the study of the nature and origin of which offers a wide 

 field of inquiry in Ontario. Before leaving the subject of the 

 distribution of animals in water, it may be noted that not only 

 do ocean currents affect the ranges of aquatic, but also of ter- 

 restrial organisms, so that, apart from their climatic influence 

 on these, they may frequently transport animals and plants to 

 new points at considerable distance from their original homes. 



(6) Relations of Animals to the Conditions of 

 Existence and to each other. 



By climate we mean temperature, pressure and other atmos- 

 pheric conditions, which do not seem to determine any con- 

 spicuous differences of form, but there are other conditions of 

 existence which do seem to be always associated with corres 



