742 General and Applied Biology 



spread general correspondence of the developmental stages in higher 

 forms with the existing adult stages of lower forms. The history of the 

 embryologic development of an individual frequently corresponds in a 

 general and broad way to the history of the development of the race as 

 a whole (Fig. 363). In other words^ the development of the individual 

 recapitulates the ancestral descent of the race; ontogeny repeats phylog- 

 eny. Read further in regard to ontogeny, phylogeny, and recapitula- 

 tion (biogenetic) theory. 



A study of the embryologic development of the heart of a bird or mam- 

 mal shows that the various stages through which its development occurs 

 really succeed each other in the same general way from the two-cham- 

 bered to a four-chambered condition, as is shown when we pass from the 

 lower vertebrates, such as the fishes, up through the amphibia, reptiles, 

 and birds to mammals (Figs. 364 and 365) . 



A similar comparative study of the brains (Fig. 366), reproductive 

 systems, skeletal systems, and digestive systems of these various vertebrates 

 shows a similar condition in which the organs of the higher animals dur- 

 ing their development pass through stages which correspond in general 

 with the larval or adult condition of similar organs in the lower forms. 

 Thus, the knowledge of the anatomy of an animal gives a broad and gen- 

 eral idea as to its type of embryologic development. 



These similarities of lower and higher types of organisms found by 

 embryologic studies suggest a similar inheritance as a basis and probably 

 an actual blood relationship between them. The only other alternative 

 is that the same "blueprint" with slight modifications and alterations 

 was used in the process of specially and individually creating each of the 

 various species. 



4. Evidences From Comparative Anatomy. — 



a. From Gross Comparative Anatomy: A detailed comparative study 

 of the anatomy of apparently different types of animals reveals a multi- 

 tude of similarities which really overbalance the more visible dissimilari- 

 ties which they possess. For instance, the differences possessed by the 

 five classes of vertebrates are relatively slight when compared with the 

 many basic and fundamental resemblances which they all possess to more 

 or less degree. 



The forelimbs of the frog, lizard, bird, horse, and man, for example, 

 are constructed on the same general structural plan and arise in a simi- 

 lar way embryologically. They are thus said to be homologous struc- 



