204 
THE DESCENT OF MAN. 
Part I. 
Nevertheless it is .certain that groups of animals have 
existed, or do now exist, which serve to connect more or 
less closely the several great vertebrate classes. We 
have seen that the Ornithorhynchus graduates towards 
reptiles ; and Prof. Huxley has made the remarkable 
discovery, confirmed by Mr. Cope and others, that the 
old Dinosaurians are intermediate in many important 
respects between certain reptiles and certain birds — the 
latter consisting of the ostrich-tribe (itself evidently a 
widely-diffused remnant of a larger group) and of the 
Archeopteryx, that strange Secondary bird having a 
Jong tail like that of the lizard. Again, according to 
Prof. Owen , 20 the Ichthyosaurians — great sea-lizards fur- 
nished with paddles — present 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 
generalised type, that is they presented diversified affi- 
nities 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 Lepidosiren and 
some few Ganoid fishes have been preserved from utter 
extinction by inhabiting our rivers, which are harbours 
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 main- 
tains that it ought to form a distinct class in the 
vertebrate kingdom. This fish is remarkable for its 
o 
20 1 Paleontology,’ 1860, p. 199. 
