VIII 
THE DEVELOPMENT OF FISHES 
THE groups of fishes have hitherto been contrasted 
_in the structures of their living and fossil forms. They 
should next be reviewed in the light of their mode of 
development ; for the developmental stages of the Shark, 
Lung-fish, or Teleostome might be expected, according 
to time-honoured belief, to furnish important evidence 
as to their descent and interrelationships. The younger 
stages of the various forms of fishes should thus suggest 
their ancestral characters: the developing Teleost should 
approach the Ganoid; the Lung-fish and the Ganoid 
should resemble their supposed elasmobranchian ancestor. 
But the embryology of fishes is in this regard very 
inconclusive, if at present in any important way sugges- 
tive. The majority of the forms, including some of the 
most important, are developmentally unknown; yet suffi- 
cient is known of the representative members of the 
groups to show the most perplexing characters. On the 
one hand, the developmental processes of forms which are 
regarded by the morphologist as closely akin seem often 
_ widely distinct; and, on the other hand, the fishes which 
_ should, a priori, exhibit an archaic mode of development 
actually present complex processes of early growth which 
can only be interpreted as highly specialized. In fact, 
there are far greater differences in the developmental plans 
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