330 



LIFE BY THE SEASHORE. 



or owl came first but enough has been said to show that 

 the matter is worth thinking about. In closing, it may be 

 well to note that while on the one hand there are naturalists 

 who believe that the primitive animals were pelagic, and 

 on the other those who believe that they were littoral, there 

 is also a third and perhaps increasing school who hold that 

 while existing pelagic and littoral animals are interlocked 

 and interrelated in a thousand different ways, we have no 

 data at present from which we can discover 

 anything of the characters of the primitive 

 forms. Even those, however, who believe 

 that the open sea was the first home of life 

 do not deny that most of the existing 

 pelagic animals have passed through a lit- 

 toral phase, and then returned to the open 

 sea. 



In the above discussion we have confined 

 ourselves to the evidence derived from In- 

 vertebrates, but those who follow the argu- 

 ment in larger works should not forget that 

 there is also a pelagic fish fauna, a pelagic 

 mammalian fauna (whales, dolphins, etc.), 

 even a pelagic insect. The last two cases 

 show that from land and air, as well as 

 FIG. 93. Sea-goose- f r0 m the shore, animals may return to the 



berry, or Pleuro- ... J 



brackia, with the easy life of the open sea. 

 ed? ta A peiagfcco?" &itol*l animals are not only interesting 

 lenterate with no on account of the question of their rela- 

 tion to pelagic forms, for we must think 

 also of their relation to the fresh -water and terrestrial 

 forms. Many shore animals live near the mouths of rivers 

 or streams, and not a few of them learn to tolerate a con- 

 siderable admixture of fresh water. By some such process 

 of gradual colonisation, we can suppose many fresh-water 

 forms to have originated. Periwinkles and some Crustacea 

 live at or near high-tide mark, and can tolerate free exposure 

 to the atmosphere ; it is reasonable to believe that in this 

 way some terrestrial Molluscs and Crustacea may have arisen 

 from littoral forms. The shore animals thus constitute a 

 most interesting group, and have relations with most of the 

 other great faunas of the globe. 



