138
THE BIOLOGY OF FISHES
.
,
The development in other shes, Elasmobfanchs rand
Dipnoi, is quite different. For one thing, the
does not come in the way and the genital organs
in Closer connection With the kidneys. As in some of the
Salmonidæ (Osmerus) the organs are free in the
cavity. (gymnoarian) and the products might escape through
'
the abdominal pores as in the latter forms.
In the mâles,,_
however, the ducts remain essentially as in the
Teleosts, whilst in the females the condition f0reshadowed '
in- Osmerus is further developed. The duct remains
anteriorly and reCeives the eggs when they fall into the cavity.
This arrangement has probably developed as a result of the ?
Closer unionof. the sexes. ,
_
'
,
the internal arrangé—’}
a're dealing with the
_
Ï'hidden—
?‘pr0greSsivelevolution. ;;The V'_Ï'formation _0f blood 'corpusclès
vascular
'
.;
system, though foreshadowed in son‘1ei=of the = Invertebrates,
now becomes an
fact.
rom this hasresulted
the division of labour, whereby the lymph system
trates on the work of feeding, repairing, and cleansing the
system.
The blood glands are the natural consequence,
and we can now trace back to the shes the origin of those
qualities which have made the higher forms of life and 7_'Ï
-
possible.
:
ï_ _ _-_
In this internal evolution within we can read no special
adaptation to particular conditions. '
The leucocytes
 :Â
; Î.
whether the
lives
_
;mtheseaoronland,and the organe they build up are
:Ofgeneralnotparücularuse The construction of organe
'
;
division of labour andled
Ë tofutherg10wth The internal phenomena of life thereafter
and differehtia—
Êtmn,accordmg
-Qf — the
centres
’ and ;
?
f
blœdglandstocentrolthewhoiesystem
taking
and d;is_- [ j , à —'
iturbmgmuencæ » :r—-J:—
-
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=