24
THE BIOLOGY OF FISHES
evolution and is possibly less efcient. Compared with
,
amphibians and reptiles it has not the blood—vessels,
_
known
the renal-portal system, which convey the
used—up blood from the bind limbs or caudal region
through theî’kidneys, and the result is that the blood is not
.
cleansed of the urates and lime salts to the same extent.
As mentioned previously, these are deposited in various
parts of the skin and body, and it is probable that bone has
arisen in the same Way.
This is not very remarkable in
itself, when we remember how low in the scale of vertebrate
life
sh stand.
They are not far removed from the
invertebrate series in _which the kidneys were of a different
and more primitive nature. In fact, as we shall see, the
excretory system of theshes remains in someways in the
'
same condition as in the ‘earliest stages of animal life.
’
_
With the
and.the clogging of the
blood—fthrough j_the wasteproducts, we mayco1m6Ct:Œe loW
level of psychic life 'Î-ÎèlioWn
;
This can
with greater
since Ïwe
=_form‘s which have made advan‘eeSin
:
:
ora—the other,*f display a higher level of intelligence and,
'
appareny, '1‘638011i11gpôWêl‘8‘. —AtleaSt, their actions reveal
many? of the mental attributes we associate usually With a
'mueh— higher stage in evolution—higher
far as the
'
structure is concerned;
5'
-
.
‘