CREATION BY EVOLUTION
its beginnings, or rather of completing the imperfect story told by fossils.
The earliest stages in this history in the human embryo are blurred out of all recognition, but if we examine the earlier history of the tadpole or, still better, that of the newt, a primitive amphibian, we can get a general idea of the history of life from the beginning. The egg, as we have seen, is a single cell in its essential structure, the same as a whole group of single-celled animals termed the Protozoa. This cell divides into many cells, which cohere together and form a little hollow ball called the blastula. Similar little balls, in which the cells have acquired green colouring matter, roll about in the waters of our ditches. The blastula becomes converted into a hollow cup called the gastrula by the pushing in of the cells at one end. The opening of the cup is called the blastopore. This opening is retained throughout life as the anus or vent of the animal, and above the anus the tail grows out. The outer layer of the cup forms the skin; the brain and the nervous system are at first mere thickenings in this layer. The inner layer forms the lining of the stomach; the rudimentary backbone is only a ridge or folding of this inner skin along its upper surface. The mouth is formed as a new opening in front; the gill slits are clefts at the sides of the throat; the eyes grow out as buds on the brain; the nose and ears are pits in the skin, and behold! we have before us no longer a swimming cup but the beginning of a tadpole, which is really a very primitive type of fish.
A study of the development of jointed animals (the Arthropoda), of the Mollusca (clams, oysters, and snails), and of the Echinodermata (starfish and sea-urchins) leads us to similar startling and fascinating results. We find that worms, arthropods, and mollusks arose from a common
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