VOUNGSOF SREP TERS 
and with abundant yolk. Correlated with the large 
size of the egg the young when hatched from it is prac- 
tically adult. Beyond a slight tooth developed upon the 
snout for the purpose of breaking the eggshell it is like 
its parent. There is nothing at all comparable to the 
larval forms of the amphibia. In these latter animals 
the eggs are not large and have not abundant yolk. 
Correlated with this is a condition unlike that of the 
reptilia. The young are born in an earlier condition ; 
and inasmuch as in that earlier condition of necessary 
incompleteness the young would be unable to lead an 
independent existence, they have been provided with 
certain organs which are of use to them only as young 
and which disappear when they reach maturity. To 
the young of an animal which leaves the egg in an im- 
mature condition, but which has special organs suited to 
a free life in that condition which later disappear, the 
term “‘lJarva”’ is applied. Many groups of the animal 
kingdom go through a larval stage. For instance the 
butterfly leaves the egg as a caterpillar, which is a larva. 
The caterpillar is not merely an imperfect butterfly. 
It has special organs of its own. Its jaws for example 
are not imperfect jaws which later develop into the 
trunk and so forth of the butterfly. They are complete 
as biting jaws and disappear when the adult condition 
is assumed. So, too, the tadpole of our common frog, 
being hatched at a stage antecedent to the appearance 
of the later developed lungs, breathes by means of 
external processes of the skin, which are the gills and 
peculiar to the larvee, disappearing when it metamor- 
phoses into a frog. Below the jaw is a sucker which 
allows it to moor itself to water plants. This structure 
is not the immature form of any structure which occurs 
in the frog. It is an organ only found during the tad- 
pole stage ; it is in fact a larval organ and its existence 
is one of the reasons for terming the tadpole a larva. 
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