A Story Outline of Evolution 



ing from the invertebrate to the vertebrate type of animals. 

 However, this is a misnomer as there are no abrupt steps in 

 evolutionary growth, but instead, there are changes so 

 gradual that they blend like the colors of the rainbow. But 

 it was this change from the invertebrate to the vertebrate 

 type that led to the more rapid development in the forms of 

 higher life. It must be remembered that nearly three- 

 fourths of all of life's history had passed before the animals 

 of this period came into being. But before passing on to 

 the life of the vertebrate animals, it is of interest to note 

 the forms of life that make up the connecting link between 

 the invertebrates and the vertebrate animals. 



Many of the oldest classes of animals known because 

 of some basic defect in their structure or their habits of life 

 have gone into a "dead end" or "blind alley" road and there 

 remained in practically the same form for millions of years 

 content to live without development. Many thousands of 

 classes have lived their lives without adaptation and have 

 passed from the scene of struggle. Others have degenerated 

 from a higher form to a lower form and have lost the 

 advancement that had been made by their ancestors. Included 

 in the classes that have failed to make progress in their 

 advancement are the star fishes, moUusks, cephalopods, sea 

 urchins and many others. The parasitic animals belong to 

 this class for no animal, regardless of how far down the 

 scale of life or up the scale of life, can live on the labors \of 

 another and, at the same time keep abreast with the school, 

 flock, pack, herd or crowd. Many of the unprogressive 

 types have constructed walls about them over which they 

 cannot climb or built a load of lime around their bodies that 



[i88] 



