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THE POPULAR SCIEXCE MONTHLY, 



progress from the germ to the adult stage present themselves to view 

 as simply meaningless facts and useless freaks and vagaries of Nature. 

 Accepting the idea favored, one may add, by every circumstance of 

 life-science much that was before wholly inexplicable becomes plain 

 and readily understood. And the view that a living beiiig's develop- 

 ment is really a quick and often abbreviated summary of its evolution 

 and descent both receives support from and gives countenance to the 

 general conclusion that life's forces tend as a rule toward progress, but 

 likewise exhibit retrogression and degeneration. If a living being is 

 found to begin its history, as all animals and j^lants commence their 

 existence, as a si:)eck of living jelly, comparable to the animalcule of 

 the pool, it is a fair and logical inference that the organisms in ques- 

 tion have descended from lowly beings, whose simplicity of structure 

 is repeated in the j^rimitive nature of the germ. If, to quote another 

 illustration, the placid frog of to-day, after passing through its merely 

 protoplasmic stage, appears before us in the likeness of a gill-breath- 

 ing fish (Fig. 1), the assumption is plain and warrantable that the frog 



Fig. 1. Develoi'ment of Frog. 



race has descended from some primitive fish stock, whose likeness is 

 reproduced with greater or less exactness in the tadpoles of the ditches. 

 Or if, to cite yet another example, man and his neighbor quadrupeds 

 (Fig. 2), birds, and reptiles, which never breathe by gills at any period 

 of their existence, are found in an early stage of development to pos- 

 sess *' gill-arches" (//), such as we naturally expect to see, and such as 

 we find in the fishes themselves, the deduction that these higher ani- 

 mals are descended from gill-bearing or aquatic ancestors admits of 



