CH. xui. ZOOLOGY. 475 



likeness in the fact that in ages long gone by they started 

 from a common source ; and every resemblance we trace, in 

 parts now used for different purposes, is only additional 

 proof of the marvellous way in which the same structures 

 are adapted to changed habits and conditions of life. The 

 classifications of animals, as given by Owen and Huxley 

 in England, and Von Baer, Gegenbaur, and Haeckel in 

 Germany, and in fact by all zoologists of our time, is 

 formed upon this conception of the actual relation of living 

 forms, and so classification becomes no longer a mere 

 arrangement for convenience, but a real statement of what 

 we know about the links which bind the animal creation 

 together. But in order to find these links an almost in- 

 credible amount of patient work must be done. It is not 

 enough to understand merely the prominent characters of 

 an animal. Its minutest structure must be known, for 

 those parts of least importance in its own life are often of 

 the greatest value to the naturalist, because they are the 

 remains of some organ which was useful to a remote ancestor. 

 And when we are once started on this road, the help 

 and suggestion which comes in from all sides is endless. 

 Mr. Romanes, for example, has found in the Medusae 

 or jelly-fish traces of a nervous system, rudiments of eyes, 

 and sacs of mineral matter, forming probably a rude hearing- 

 apparatus, while on the other hand a rudimentary unpaired 

 eye has been found in Lizards very nearly allied to the eye 

 of invertebrate animals. Thus we find constantly new links 

 between the two divisions of the animal kingdom, and it is 

 probable that in time the earliest beginnings of organs 

 similar to our own may be traced in extremely simple 

 invertebrate animals, and from thence upwards through the 

 various branches of the animal kingdom till they reach theil 

 highest development in man. 



