THE DEVELOPMENT OF THE ANIMAL WORLD 67 



has already run through several volumes, and a great 

 variety of forms is found. 



In view of this scantiness of direct evidence we will 

 not linger long over the early stages of animal evolution. 

 We have, however, two lines of indirect evidence with 

 which we can reconstruct the story to some extent. 

 The first means is to arrange the lowest of existing 

 animals in the order of their degree of organisation, and 

 see how far they will suggest the line of development. 

 It often occurs to readers to see an objection to the 

 principle of evolution in the fact that animals of the 

 very simplest type are found in nature to-day much as 

 we assume them to have been fifty million years ago. 

 Bacteria were at work on the trees in the Carboniferous 

 forests as they are at work in the forest to-day. Indeed, 

 the Amoeba that we find to-day in the pond or the rain- 

 gutter seems to be an almost unchanged descendant of one 

 of the earliest forms of animal life. But a simple explana- 

 tion can soon be found. The lowest environment remains 

 suited to the lowest forms of life. When the more gifted 

 relatives of an animal pass on to a different environment 

 or diet, the old environment remains for the unchanged. 

 The struggle for life does not tend to suppress a species, 

 but to keep down its numbers. The water is still an 

 ample home for myriads of fishes when some of their 

 number have advanced to the land. It would not be an 

 advantage for all to turn into land animals. 



Hence it is that we have still animals at every stage 

 of organisation. The microscopic Amoeba, gliding like a 

 drop of sluggish oil along the slide of the microscope, 

 merely pushing out broad and ever-changing projections 

 of its substance as a vague suggestion of limbs, and 

 wrapping itself round a particle of food or even ar 



