196 THE DESCENT OF MAN. [Part L 



seen that the Ornithorhynchus graduates toward reptiles ; 

 and Prof. Huxley has made the remarkable discovery, 

 confirmed by Mr. Cope and others, that the old Dinosau- 

 rians are intermediate in many important respects between 

 certain reptiles and certain birds — the latter consisting of 

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

 nant of a larger group) and of the Archeopteryx, that 

 strange Secondary bird having a long tail like that of the 

 lizard. Again, according to Prof. Owen, 20 the Ichthy- 

 osaurians — great sea-lizards furnished with paddles — pre- 

 sent many affinities with fishes, or rather, according to 

 Huxley, with amphibians. This latter class (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 highly-generalized type, that is, they pre- 

 sented diversified affinities with other groups of organisms. 

 The amphibians and fishes are also so closely united by 

 the Lepidosiren, that naturalists long disputed in which 

 of these two classes it ought to be placed. The Lepido- 

 siren and some few Ganoid fishes have been preserved 

 from utter extinction by inhabiting our rivers, which are 

 harbors of refuge, bearing the same relation to the great 

 waters of the ocean that islands bear 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 maintains 

 that it ought to form a distinct class in the vertebrate 

 kingdom. This fish is remarkable for its negative charac- 

 tors ; it can hardly be said to possess a brain, vertebral col- 

 umn, or heart, etc. ; so that it was classed by the older 

 naturalists among the worms. Many years ago Prof. 

 Goodsir perceived that the lancelet presented some affini- 

 ties with the Ascidians, which are invertebrate, hermaphro- 



20 ' Palaeontology,' 1860, p. 199. 



