ECONOMY or THE,
135“
of, and for thispùrpose, in_Higher Vertebratès, the kidneys
are speciallyorgani3ed. As might; be expected,-the shes
show axvery early stag'ein the development of this apparatus.
Excretion' may be performed in two dierent ways .;
by means of “
wandering cells” Without
organ,
‘
or'by tubules massed together—and closely,cbnnected Withan '
assemblage of blood capillaries,and opening
—
by a special ductÏ or by ducts.f
wandering cells is certainly the original form of the sep‘araê‘ -
tion of metabolic ehd-produCts
”
(Sterpell and
1916). These wandering cells, the
of other cells laden With excretion andendèavoür to con_vey
them out'of the body, either by denite channels (nephridia), ‘
if such are present, or through the skin or into the body
Cavity—wheæver they can be deposited without harming the
internal economy of the organism. Some Invertebratès,
e.g._-the insects, show various accumulations 'of' these
,
wanderii1g cells, Which” have been unable to penetrateî the…
1
hard Cuticle (nephrocytes, pericardial cells).
'
_
‘
,
The shes,
ï especially the Teleosts, _,shOW {Very high
_
,
development
=o£ excr6tion,j_
a ,
.,
.
"
(argentéuai) *aÿd
thptnm Inllpbbltytthtnth
skin of inorganic
[; Ï
,
is of the same nature; leading to
‘
-
denticles, and plates of various
process has
Ï ‘
become an integral part of the organisation of the'sh, and
Several things are noteworthy. In the Teleosts the scales
:
are laid down in the skin before the kidneys (meSonephros)
are developed. Secondly, when the circulation of the. blood
ï
is disturbed, as by the compression and reduction, ofthe
.
gills, ordinary scales are replaced
plates_;whlch
grow in & similar}manefffofthe01drh0mbmscales(33m
.
.
GaStrosteusandxthe.Pipe—shes')èälfr
°
In theTunnyändÿïsèmè @îhéfs. 0nlyêheadkï‘ïneyls L:
butaremarkableplems°fcaPlafo1°°d'
vesselsextendsnbetweenthemusclesP°SœrmYWherethe