Geographical Distribution. 183 



an ancient sea, e.g. many of the molluscs of Lake 

 Tanganyika; (c) the cosmopolitan forms which are 

 readily transported on birds' feet and otherwise from 

 one water-basin to another; and (d), if any remain, the 

 autochthonous or aboriginal forms which are not repre- 

 sented by any near relatives outside of fresh water. 



The question of the origin of land animals was 

 present to the inquiring minds of the Greek philoso- 

 phers, but, so far as we know, it has not 



j ' Terrestrial. 



been seriously tackled except by one natu- 

 ralist, Prof. H. Simroth, in his Entstehung der Land- 

 thiere (1891). And notwithstanding the author's in- 

 genuity and learning, the work does not convey the 

 impression of a problem solved. 



Slowly, and it may have been by zigzag paths, or- 

 ganisms wandered inland from the shores of sea and 

 estuary and river, or became able to survive the drying 

 up of landlocked basins. Simroth seeks to show that 

 hard skins, cross-striped muscle, brains worthy of the 

 name, red blood, and so on, were acquired as the 

 transition to terrestrial life was effected. 



Besides the five main life-areas littoral, pelagial, 

 abyssal, fluvial, and terrestrial minor ones might be 

 distinguished. Much work of interest has been recently 

 done in regard to the organisms found in brackish 

 water, in caves, underneath the ground, in the air, 

 within other organisms, and so on. But to discuss 

 these is beyond our scope. 



It is at least stimulating to think over the possible 

 historical relations of the great faunas which we have 

 alluded to above. Various possibilities may Evolution 



be Stated. of Faunas. 



(a) According to Moseley, "The fauna of the coast 

 has not only given origin to the terrestrial and fresh- 

 water faunas, it has throughout all time, since life 

 originated, given additions to the pelagic fauna in 

 return for having received from it its starting-point. It 

 has also received some of these pelagic forms back 

 again, to assume a fresh littoral existence. The terres- 

 trial fauna has returned some forms to the shores, such 

 as certain shore-birds, seals, and the polar bear; and 



