182 VARIETY OF MOLLUSCA. 



animal kingdom replete with interest, and pregnant with 

 overwhelming proofs of design and wisdom. The study 

 of these creatures is, happily, not restricted within nar- 

 row limits ; on the contrary, opportunities for engaging 

 in it are widely extended. Climate operates on the 

 geographical distribution of particular species ; but, as 

 there is more uniformity of temperature in the waters 

 of the ocean than in the air of the land, the diffusion of 

 man}- marine mollusks is extensive. 



Some of these creatures become most fully developed 

 in warm latitudes, and to these most of their species 

 are exclusively confined. Two instances are mentioned 

 in which mollusks diminish in size as they follow the 

 coasts of New Holland to King George's Sound, and 

 entirely disappear beyond them. Nearly all the species 

 of South American shells differ from those of the Indian 

 Archipelago in the same latitudes ; and peculiar species 

 have been obtained on the shores of many of the 

 islands of the South Pacific. Means of limitation, in 

 certain cases, may be easily traced. The mollusks of 

 the West Indian seas cannot enter the Pacific, without 

 passing round through the inclement climate of Cape 

 Horn. Currents constantly flowing in a particular 

 course, and the influx of great bodies of fresh water 

 at certain points, limit the extension of many species. 



