Page Ten 



EVOLUTION 



January, 1938 



out, the ability to grow and multiply, and the ability to 

 adapt themselves to their surroundings. Every living thing 

 in this pool, tor example, is composed of six chemical ele- 

 ments, always the same six, with which few or many others 

 may be combined. If we should try to imagine a machine 

 of some sort which could stoke its own engine, oil its own 

 gears, repair a break, and finally reproduce other machines 

 like itself, we should realize how remarkable are the powers 



Courtesy American Musewm of Natural History 

 A Hydroid Colony 



of repair, of growth and reproduction in living things 

 which we take so much for granted. 



Returning to our tide-pool we find many conspicuous 

 examples of the way in which animals are adjusted with 

 such intricate nicety to the conditions of their environ- 

 ment. To succeed in any environment, the animal must 

 be able to secure food and oxygen, to protect itself from 

 enemies or adverse conditions, and to reproduce its kind. 

 Animals of different kinds, even in the same environment, 

 meet these problems in various ways. The rock barnacle 

 lives secure within its shell, the roof of which is tightly 

 closed when the tide recedes. But if you splash the water 

 in the pool, you may see the peak of the roof open, and 

 small feathery processes reach out and wave about in the 



water to gather in food. The snails which crawl slowly 

 over the rocks will at low tide pull themselves entirely 

 within their shell, which may often be closed completely 

 by a little horny plate, making them secure against attack 

 or drought. Turn a starfish over, and it immediately sends 

 out hundreds of thread-like projections which touch the 

 adjacent rock; the threads shorten, and presto — the animal 

 is right side up. Touch the crown of tentacles of the 

 sea-anemone or try to pull it off the rock ; the animal will 

 contract into a slippery ball, and numerous stinging threads 

 like white cotton libers will protrude from many pores. 



One other characteristic of living things remains to be 

 briefly explained, namely definiteness ot organization. A 

 plant or animal body can be resolved into elements or 

 microscopic units which are called cells. They are not 

 little hollow cases, as the name implies, but extremely 

 minute units of living matter called protoplasm, with a 

 peculiar central body or nucleus. These cells are of differ- 

 erent shapes, being much elongated in muscle and nerve 

 cells, disc-like in blood cells, and spherical in egg cells. 

 The living matter composing a cell appears under the 

 microscope as a tiny mass of granular jelly-like material, 

 containing the spherical nucleus, and surrounded usually 

 by a thin membrane or cell-wall. It was of this funda- 

 mental protoplasm that Huxley wrote in his famous essay 

 "The Physical Basis of Life". Many experiments upon 

 cells have been made which demonstrate that the nucleus 

 is essential for the life of the cell, and that certain peculiar 

 bodies called chromosomes, which it contains, are the bear- 

 ers of the hereditary characteristics from one generation 

 to the next. 



The animals that I have mentioned above make their 

 home along the continental shelf, a sort of gently sloping 

 extension of every continent, with relatively shallow water. 

 Here is a region of turbulence, of movements of tide, of 

 dashing surf, of warmth and sunlight and plenty of food.. 

 The shore is "noisy with the conjugation of the verb — 

 to eat". Other regions of the sea also have their inhabi- 

 tants. On the surface are myriads of tiny floating creatures, 

 food for larger animals. Further down are the swimmers, 

 great sharks and other kinds of fishes. Down in the re- 

 mote depths live many kinds of strange fishes where no 

 sunlight penetrates, where the pressure is enormous and 

 the temperature is near freezing. 



AH these creatures, from their earliest history, have made 

 the seas their home. But strangely enough, two of the 

 most impressive types that swim the seas, namely the seals 

 and whales, evolved from land animals and are really 

 mammals as their body build shows, with only superficial 

 resemblance to fishes. 



Book Reviews 



EXPLORING THE HEAVENS. By 

 Clyde Fisher. 223 pp. New York: 

 Thomas Y. Crowell Co. $2.50 

 Modesty is undoubtedly the reason 

 why Qyde Fisher, Curator of Astron- 

 omy at the American Museum of Nat- 

 ural History for many years, respon- 

 sible for the erection of the Hayden 

 Planetarium and now its Curator, has 

 not long ago published a book on 

 popular astronomy. For a long time 

 he has been in demand for lectures on 

 the subject. For years he has been 



visiting the observatories throughout 

 the world, four times he has taken 

 part in solar eclipse expeditions. He 

 has studied meteor craters right on the 

 ground here and in Europe, and has 

 helped bring together the finest col- 

 lection of meteorites in the world. Yet 

 this is his first book on astronomy. 



It does not attempt the whole wide 

 range of the subject, but limits itself 

 very largely to the solar system, and to 

 the stars only as the naked eye and 

 the small telescope sees them. In 

 short, it presents the subject much as 

 the Planetarium can present it. Add 



chapters on the Origin of Our Solar 

 System, and A Glimpse of Relativity, 

 accounts of the great observatories, 

 and of the Hayden Planetarium, rather 

 full details on eclipse experiences and 

 meteor craters, and you have a wholly 

 delightful and clear account of the 

 Earth and Neighbor Worlds, the Sun 

 and Moon, Meteors and Comets, the 

 changing seasons with their pageant of 

 constellations and mythology. 



As an introduction to modern as- 

 tronomy the book is outstanding. It 

 is especially to be commended for its 

 many select and beautiful illustrations, 



