.'
)
ADAPTATION
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'
257
and Eagle-rays have a strong spine in their tail
Which they use to cut up. their victims, and if one spine is
lost another is developed to replace it. ' The Climbing
Perch makes its way overland by means of the spines on
the .gill—cover and ns, and other species of the same‘fà1ily
hold on to stones in running streams. But, of course,. the
same end can be attainedin other wa‘yswithout—spines.……
In some cases the spines are used as =weapons
of o"enée
and defence—for example,by the small Gasterosteus.(Stickle—
back) and Osphromenidæ when;engaged in ghting with
one
another, but we can zhardly believeÎthat they were
-—:developed for. thatpurpose.
many shes
most deadlyspinœ, butare not known to .use them; -.The
Connon-Weevers of the shore are peaceful shes and have
no
mûre need of spines than the Plaice they live with.
If these spines are accidentally stepped on, however, they
cause a serious wound made more dangerous by the poison—
ous
mucous
secretion
__
which gets into the wound. _The
pecùliarity of the “spines which have poisonous glands gor
sacs*.conne‘cted with them_is,that they are loose in the—tissues,
where usually theÿ= are xed,._ It; is, probable, therefore, -
rubbingi ,o£:—-the,loose Spine on the“
to, the development of glandular
cells-"aboveï,andÿ:b'elowf—jUSt asthe eyes of some: Sheshave;
_
’
The spinesof the rst dorsal n‘in the Weeverareloos‘er
than usual, but the glands are small and, in-the rays behind
the rst, mainly detached cells of the surrounding epithelium. As a sign of some disruptive agent at work, the skin
"covering the spines is pigmented a deep black.
Toad—shes (Batrachus) show another variety of
spines. The agency
at work is presumablÿ
'
thesame, but the opercular spine is perforated, that is,,,the
loOses'piné has worked moreoh the cells at the base and the
,
acid secretion has
itsWaÿoutwards
;
Owing:to
the ,:spinès of Trachinus; and
_
'
'
Batrachùs haVe
the poison ‘fangs
colubrine snakes
vipers,respectively…
,
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,