GILES AND GIEEsOLE ET. 
glands of the amphibian. On the other hand, the also 
burrowing Cececilians already referred to have scales. 
But though the Ccecilians have scales they have also 
the mucous glands of other amphibia. It is doubtful, 
however, whether some of the heavily armoured am- 
phibia of remote antiquity, the Labyrinthodonts and 
their allies, could have possessed much in the way of 
slime-producing glands. 
As to the nature of the limbs, which certainly dis- 
tinguish so far as their characters go, the Menobranchus 
and the Lacerta, there is no possibility whatever of 
drawing by their help a hard and fast line between 
amphibia and reptilia generally. In both groups we 
have reduction of number of digits and of the limbs 
themselves, culminating in both divisions alike in com- 
pletely apodous forms. When however we come to 
the respiratory apparatus, we find at once a difference 
which holds good throughout the whole reptilian and 
amphibian series with insignificant exceptions. We 
may safely state that no reptile ever breathes by means 
of gills, and that in no reptile is there ever any perman- 
ence of the gill clefts. On the other hand in amphibia 
there may be a sharing of the respiratory functions for 
life between gills and lungs, and at some time of its life 
the amphibian breathes only by gills. Moreover there 
is often a persistence of the gill clefts up to mature life, 
a feature which the amphibian clearly shares with the 
fish ; in which these clefts, putting the outside world 
into communication with the pharynx, always persist. 
In the fish these clefts are divided by bars of cartilage 
which bear vascular tufts which are the gills. In all the 
higher vertebrates the embryo shows traces of these 
clefts; but in the amphibia only do they ever persist 
into adult life. This leads us to the consideration of the 
development of the amphibia as compared with that 
of the reptilia. In the latter the egg is always large 
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