DISTRIBUTE INSECT VARIETY. 



253 



CHAPTER VII. 



THE FOREGOING PHENOMENA SUPPLEMENTED BY MIGRATION, WHICH 

 INDUCES VARIATION AND NATURAL SELECTION. 



" Densior Ws tellus, elementaque grandia traxit ; 

 Et pressa est gravitate sui. Circumfluus humor 

 Ultima possedit, solidumque coercuit orbem. 



Sic ubi dispositam, quisquis fuit ille deorum, 

 Congeriem secuit, sectamque in membra redegit, 

 Principio terram, ne non ffiqualis ab omni 

 Parte foret, magni speciem glomeravit in orbis. 

 Turn freta dififudit, rapidisque tumescere ventis 

 Jussit, et ambitaj circumdare littora terrse. 

 Addidit et f ontes, immensaque stagna, lacusque ; 

 Fluminaque obliquis cinxit declivia ripis : 

 Qusp, diversa locis, partim sorbentur ab ipsa, 

 In mare perveniunt partim, campoque recepta 

 Liberioris aqua?, pro ripis littora pulsant. 

 Jussit et extendi campos, subsidere valles, 

 Fronde tegi silvas, lapidosos surgere montes. 

 Utque dute dextra caelum, totidemque sinistra 

 Parte secant Zonte, quinta est ardentior illis ; 

 Sic onus inclusum numero dlstinxit eodem 

 Curadei: totidemque plag;e tellure premuntur. 

 Quarum qua3 media est, non est habitabilis testu : 

 Nix tegit alta duas : totidem inter utramque locavit." 



Ovid, "Metamorphoses,^^ i. 5. 



The cosmogony of our globe has engaged the attention of 

 the philosopher in every age ; but as the stream of Science rolled 

 onward new powers accumulated to be repeatedly enlisted in its 

 investigation. The astronomer of the day, who at midnight, 

 looking out on the confines of space and time, observes a nebulous 

 vapour gyrating in interstellar ether, first descries the portentous 

 nucleus of a phantom world. The spectroscopist, in the rainbow 

 hues refracted from his battery of prisms, then seeks certain dark 

 lines, where he reads the qualities of some of the hundred simple 

 elements entering into the composition of our globe, in gaseous, 



