THE GENEALOGY OF MAN. 225 



eral of the great vertebrate classes more or less closely. 

 We have seen that the Ornithorhynchus graduates toward 

 reptiles ; and Professor Huxley has discovered, and is 

 confirmed by Mr. Cope and others, that the Dinosaurians 

 are in many important characters intermediate between 

 certain reptiles and certain birds — the birds referred to 

 being the ostrich-tribe (itself evidently a widely-diffused 

 remnant of a larger group) and the Archeopteryx, that 

 strange Secondary bird, with a long, lizard-like tail. 

 Again, according to Professor Owen, the Ichthyosaurians 

 — great sea-lizards furnished with paddles — present many 

 affinities with fishes, or rather, according to Huxley, 

 with amphibians ; a class which, including in its highest 

 division frogs and toads, is plainly allied to the Ganoid 

 fishes. These latter fishes swarmed during the earlier 

 geological periods, and were constructed on what is called 

 a generalized type, that is, they presented diversified affini- 

 ties with other groups of organisms. The Lepidosiren is 

 also so closely allied to amphibians and fishes that natural- 

 ists long disputed in which of these two classes to rank it ; 

 it, and also some few Ganoid fishes have been preserved 

 from utter extinction by inhabiting rivers, which are har- 

 bors of refuge, and are related to the great waters of the 

 ocean in the same way that islands are to continents. 



Lastly, one single member of the immense and diver- 

 sified class of fishes, namely, the lancelet or amphioxus, 

 is so different from all other fishes, that Hackel main- 

 tains that it ought to form a distinct class in the verte- 

 brate kingdom. This fish is remarkable for its negative 

 characters ; it can hardly be said to possess a brain, ver- 

 tebral column, or heart, etc., so that it was classed by 

 the older naturalists among the worms. Many years ago 

 Professor Goodsir perceived that the lancelet presented 

 some affinities with the Ascidians, which are invertebrate, 

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