the past condition of organic nature-第5章

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similarity。

I　explained　what　I　meant　by　ORDERS　the　other　day；　when　I　described　the
animal　kingdom　as　being　divided　in　sub…kingdoms；　classes　and　orders。　If
you　divide　the　animal　kingdom　into　orders；　you　will　find　that　there　are
about　one　hundred　and　twenty。　　The　number　may　vary　on　one　side　or　the
other；　but　this　is　a　fair　estimate。　　That　is　the　sum　total　of　the　orders
of　all　the　animals　which　we　know　now；　and　which　have　been　known　in　past
times；　and　left　remains　behind。

Now；　how　many　of　those　are　absolutely　extinct？　　That　is　to　say；　how　many
of　these　orders　of　animals　have　lived　at　a　former　period　of　the　world's
history；　but　have　at　present　no　representatives？　　That　is　the　sense　in
which　I　meant　to　use　the　word　〃extinct。〃　　I　mean　that　those　animals　did
live　on　this　earth　at　one　time；　but　have　left　no　one　of　their　kind　with
us　at　the　present　moment。　　So　that　estimating　the　number　of　extinct
animals　is　a　sort　of　way　of　comparing　the　past　creation　as　a　whole　with
the　present　as　a　whole。　　Among　the　mammalia　and　birds　there　are　none
extinct；　but　when　we　come　to　the　reptiles　there　is　a　most　wonderful
thing：　out　of　the　eight　orders；　or　thereabouts；　which　you　can　make　among
reptiles；　one…half　are　extinct。　　These　diagrams　of　the　plesiosaurus；
the　ichthyosaurus；　the　pterodactyle；　give　you　a　notion　of　some　of　these
extinct　reptiles。　　And　here　is　a　cast　of　the　pterodactyle　and　bones　of
the　ichthyosaurus　and　the　plesiosaurus；　just　as　fresh　as　if　it　had　been
recently　dug　up　in　a　churchyard。　Thus；　in　the　reptile　class；　there　are
no　less　than　half　of　the　orders　which　are　absolutely　extinct。　　If　we
turn　to　the　'Amphibia'；　there　was　one　extinct　order；　the
Labyrinthodonts；　typified　by　the　large　salamander…like　beast　shown　in
this　diagram。

No　order　of　fishes　is　known　to　be　extinct。　　Every　fish　that　we　find　in
the　stratato　which　I　have　been　referringcan　be　identified　and
placed　in　one　of　the　orders　which　exist　at　the　present　day。　　There　is
not　known　to　be　a　single　ordinal　form　of　insect　extinct。　　There　are
only　two　orders　extinct　among　the　'Crustacea'。　　There　is　not　known　to
be　an　extinct　order　of　these　creatures；　the　parasitic　and　other　worms；
but　there　are　two；　not　to　say　three；　absolutely　extinct　orders　of　this
class；　the　'Echinodermata'；　out　of　all　the　orders　of　the　'Coelenterata'
and　'Protozoa'　only　one；　the　Rugose　Corals。

So　that；　you　see；　out　of　somewhere　about　120　orders　of　animals；　taking
them　altogether；　you　will　not；　at　the　outside　estimate；　find　above　ten
or　a　dozen　extinct。　　Summing　up　all　the　orders　of　animals　which　have
left　remains　behind　them；　you　will　not　find　above　ten　or　a　dozen　which
cannot　be　arranged　with　those　of　the　present　day；　that　is　to　say；　that
the　difference　does　not　amount　to　much　more　than　ten　per　cent。：　and　the
proportion　of　extinct　orders　of　plants　is　still　smaller。　　I　think　that
that　is　a　very　astounding；　a　most　astonishing　fact；　seeing　the　enormous
epochs　of　time　which　have　elapsed　during　the　constitution　of　the　surface
of　the　earth　as　it　at　present　exists；　it　is；　indeed；　a　most　astounding
thing　that　the　proportion　of　extinct　ordinal　types　should　be　so
exceedingly　small。

But　now；　there　is　another　point　of　view　in　which　we　must　look　at　this
past　creation。　　Suppose　that　we　were　to　sink　a　vertical　pit　through　the
floor　beneath　us；　and　that　I　could　succeed　in　making　a　section　right
through　in　the　direction　of　New　Zealand；　I　should　find　in　each　of　the
different　beds　through　which　I　passed　the　remains　of　animals　which　I
should　find　in　that　stratum　and　not　in　the　others。　　First；　I　should
come　upon　beds　of　gravel　or　drift　containing　the　bones　of　large
animals；　such　as　the　elephant；　rhinoceros；　and　cave　tiger。　　Rather
curious　things　to　fall　across　in　Piccadilly！　　If　I　should　dig　lower
still；　I　should　come　upon　a　bed　of　what　we　call　the　London　clay；　and　in
this；　as　you　will　see　in　our　galleries　upstairs；　are　found　remains　of
strange　cattle；　remains　of　turtles；　palms；　and　large　tropical　fruits；
with　shell…fish　such　as　you　see　the　like　of　now　only　in　tropical
regions。　　If　I　went　below　that；　I　should　come　upon　the　chalk；　and　there
I　should　find　something　altogether　different；　the　remains　of
ichthyosauri　and　pterodactyles；　and　ammonites；　and　so　forth。

I　do　not　know　what　Mr。　Godwin　Austin　would　say　comes　next；　but　probably
rocks　containing　more　ammonites；　and　more　ichthyosauri　and　plesiosauri；
with　a　vast　number　of　other　things；　and　under　that　I　should　meet　with
yet　older　rocks；　containing　numbers　of　strange　shells　and　fishes；　and
in　thus　passing　from　the　surface　to　the　lowest　depths　of　the　earth's
crust；　the　forms　of　animal　life　and　vegetable　life　which　I　should　meet
with　in　the　successive　beds　would；　looking　at　them　broadly；　be　the　more
different　the　further　that　I　went　down。　　Or；　in　other　words；　inasmuch
as　we　started　with　the　clear　principle；　that　in　a　series　of
naturally…disposed　mud　beds　the　lowest　are　the　oldest；　we　should　come
to　this　result；　that　the　further　we　go　back　in　time　the　more　difference
exists　between　the　animal　and　vegetable　life　of　an　epoch　and　that　which
now　exists。　　That　was　the　conclusion　to　which　I　wished　to　bring　you　at
the　end　of　this　Lecture。







End