so 
LECTURE VIIL 
Rs confinement. During the first six or eight 
hours from its birth, it is observed to grow 
nearly as much in proportion as in fifteen or 
twenty days afterwards. In the young ani« 
mal before it has left the egg, the pulsations or 
beatings of the heart amount to about forty in 
a minute; but immediately after hatching, they 
are increased to the number of sixty in a minute. 
Young fish, in this very diminutive state, are so 
transparent as to exhibit with great distinctness 
the course even of their larger blood-vessels. In 
the work of Dr. Bloch we find a good representa- 
tion of a fish in this state, viz. the Common 
Barbel. 
The age of fish is, according to Linnseus, 
determinable from the number of concentric cir- 
cles of the vertebrae or joints of the back-bone, in 
the same manner as that of trees is supposed to 
be from the concentric circles of the wood. Leew- 
enhoeck used to imagine that the age of fish might 
be determined from the concentric circles or 
fibres of the scales ; but perhaps it may admit of 
much doubt whether either of these opinions be 
true. 
After this general survey of fishes as a tribe. 
