54 EVOLUTION OF TO-DAY. 



It is almost hopeless to attempt to give to any 

 one not acquainted with the subject, any thing like 

 a complete understanding of even the general bear- 

 ings of the question. It is useless to try to give 

 instances, because they are significant only from 

 their abundance. To show how many features man 

 has in common with the lower animals ; to show 

 how the abnormalities of his body are readily ex- 

 plained by reference to other vertebrates ; to mention 

 the fact that the human embryo possesses gill slits 

 at the side of the neck like those of the fish, and 

 has a similar distribution of blood-vessels ; to show 

 that the highly developed mouth parts of the crab 

 are simply modifications of a primitive type of 

 appendage existing in all Crustacea; that there is 

 every stage from a simple hydroid bearing sexual 

 organs to a free swimming jelly fish ; and to bring 

 forward an unlimited number of other similar facts, 

 means nothing to the general reader, or indeed to 

 any one except those already familiar with the facts 

 from personal knowledge. Or if they do mean any 

 thing, they are looked upon as simple instances of 

 the acknowledged fact that there is in nature a pos- 

 sibility of classification, and that animals show 

 homologies with each other. It is needless to 

 attempt to show how universal is this principle of 

 homology in animate nature, for its existence will 

 be everywhere acknowledged. The real question 

 to be raised, as far as this subject concerns evolution, 

 is, not as to what organs are homologous in different 

 animals, nor as to what may be the true classifica- 

 tion, but what does homology mean, and why should 



