220 



THE RISE OF ANIMAL LIFE 



is so well developed that an animal may 

 match its background almost perfectly ( see 

 p. 430). It was once thought that the chro- 

 matophores were controlled by the nervous 

 system, but it is now known that they are 

 controlled by the secretions from a tiny 

 gland, the sinus gland, located in the eye 

 stalk. If it is removed, the spread of pig- 

 ment granules in the chromatophores is af- 

 fected so that the crustacean fails to show 

 normal color change as a result. If the sinus 

 gland is replaced in the body of the crus- 

 tacean, the normal action of the chromato- 

 phores is restored. The same hormone also 

 regulates the molt and affects the deposi- 

 tion of calcium salts in the exoskeleton; oth- 

 ers affect heart action and carbohydrate 

 metabolism. Research reveals that hor- 

 mones are produced by the central nervous 

 system as well as the sinus gland. 



THE INSECTA 



Stories concerning the ravages of insects 

 are as old as man himself; such stories 

 found their way into the earliest writings 

 including the Bible. This was primarily be- 

 cause of the competition existing between 

 man and the insects, for the insects con- 

 sume the food man intended for his own 

 use. They have caused devastating famine 

 in many parts of the world, and even today 

 they torment man as well as other animals. 

 A trip through a boggy or swampy region 

 on a humid summer evening will bring any- 

 one to the sudden realization tliat the in- 

 sects appear to have a rather secure place 

 even in our modern civilization. Despite 

 constant war upon them, they still persist 

 and the cost of keeping insects under con- 

 trol is nearly one and a half billion dollars 

 each year. A traveler who crosses a state 

 border is often subjected to inspection in 

 order to determine whether or not he is 

 carrying any insect which might add to the 

 long list of "bed fellows" that the state 

 already harbors. It has been truly said that 



man's big battle today is being fought 

 against the six-legged little beast which, if 

 left unhampered, could soon overwhelm 

 man and his civilization. 



There are over 700,000 species, several 

 times more than all other species of animals 

 put together. How is it, that these small 

 animals have so outstripped all other forms 

 of life? First of all, their rigid exoskeleton 

 has enabled them to invade the air and 

 support themselves outside of water. This 

 waxy covering prevents desiccation, an es- 

 sential feature for an animal that divorces 

 itself completely from an aquatic existence. 

 They have become so successful in their air 

 environment that they have conquered all 

 possible regions — the only invertebrates 

 that have taken to the air. They burrow in 

 the ground and have returned to both fresh 

 and brackish waters, but avoid the sea. 

 They live on and in the bodies of plants and 

 animals, becoming in some instances seri- 

 ous parasites. They suck the juices of plants 

 and the blood of animals, and often feed 

 upon other species of their own group. This 

 is nature's way of maintaining a balance 

 among animals. This has been hailed and 

 encouraged by man as a method of biologi- 

 cal control. For example, certain ladybird 

 beetles are grown by the million and 

 planted on citrus fruit trees that are in- 

 fested by the destructive cottony cushion 

 scale insect. The beetles feed upon the 

 pests, thus keeping them under control. 



The wino-s of the insects have made it 

 possible for them to travel long distances, 

 thus not only increasing their ability to find 

 food but also to spread themselves to new 

 areas where they might thrive more suc- 

 cessfully. Fortunately, present-day insects 

 have never attained any great size, al- 

 though certain fossil forms did reach a wing 

 spread of more than 2 feet. Most present day 

 species range between one-eighth to one- 

 and-a-half inches in length. There is a South 

 American beetle which is about 5 inches 

 long and some tropical moths have a wing 



