66 The Outline of Science 



Church pictures the beginning of a fixed vegetation a very mo- 

 mentous step in evolution. It was perhaps among this early 

 vegetation that animals had their first successes. As the floor of 

 the sea in these shallow areas was raised higher and higher there 

 was a beginning of dry land. The sedentary plants already spoken 

 of were the ancestors of the shore seaweeds, and there is no 

 doubt that when we go down at the lowest tide and wade cau- 

 tiously out among the jungle of vegetation only exposed on such 

 occasions we are getting a glimpse of very ancient days. This 

 is the forest primeval. 



The Protozoa 



Animals below the level of zoophytes and sponges are called 

 Protozoa. The word obviously means "First Animals," but all 

 that we can say is that the very simplest of them may give us 

 some hint of the simph'city of the original first animals. For it is 

 quite certain that the vast majority of the Protozoa to-day are 

 far too complicated to be thought of as primitive. Though most 

 of them are microscopic, each is an animal complete in itself, with 

 the same fundamental bodily attributes as are manifested in 

 ourselves. They differ from animals of higher degree in not 

 being built up of the unit areas or corpuscles called cells. They 

 have no cells, no tissues, no organs, in the ordinary acceptation 

 of these words, but many of them show a great complexity of 

 internal structure, far exceeding that of the ordinary cells that 

 build up the tissues of higher animals. They are complete living 

 creatures which have not gone in for body-making. 



In the dim and distant past there was a time when the only 

 animals were of the nature of Protozoa, and it is safe to say that 

 one of the great steps in evolution was the establishment of three 

 great types of Protozoa: (a) Some were very active, the 

 Infusorians, like the slipper animalcule, the night-light 

 (Xoctiluca), which makes the seas phosphorescent at night, 



the deadly Trypanosome, which causes Sleeping Sickness. 



