48 UNIVERSAL EVOLUTION 



from the simple to the complex. These are the 

 cardinal principles of the theory of evolution. 



MORPHOLOGY. Members of the same class of organ- 

 isms resemble each other in the general plan of their 

 organization. This is unity of type. This is morphology. 

 Darwin says, "What can be more curious than that the 

 hand of man, that of a mole, the leg of a horse, the 

 paddle of a porpoise, and the wing of a bat, should all 

 be constructed on the same pattern; should include 

 similar bones, in the same relative positions ? " In some 

 degree all animals are alike in some points, not only in 

 form, but in growth. 



A tiny round cell, in the embryo, as said before, is 

 common to all, at first. From that period, to the adult 

 form, there are innumerable points of homology, and 

 more of analogy. The embryological form, common to 

 all animals, is the first to be developed, in any verte- 

 brate ; this is the formation of a round ball of cells held 

 together by a membrane, the gastrula. Then follow, 

 in regular order, in the same embryo, as it develops, 

 the structures common to the embryos of the radiata, 

 articulata, mollusca, and then the vertebrata; and 

 lastly, appear the characteristics marking the species 

 to which the embryo belongs. 



RUDIMENTARY ORGANS. And, on the upward de- 

 velopment, each species carries with it, in vestigial 

 form, many structural organs, useful in the lower 

 forms, but useless, or even harmful in the higher. In 

 the human body, we have hair covering the foetus, and 

 shed prior to birth ; the thymus gland ; the muscles 

 moving the scalp, the ears, and other parts of the skin ; 

 the peculiar fold in the tip of the ear ; the hair on the 

 arms ; the valves in the horizontal, and not in the per- 

 pendicular veins ; the pineal gland in the brain ; the 



