DESIGN IN THE ORGANIC WORLD. 459 



the Mediterranean, — with the singular exception of the deep-sea 

 type found to the west of Ireland, which is probably a survival 

 from the warmer climate of some former epoch. And among the 

 specimens collected by the C/ialienger on the Fiji reef, I have 

 found a marked difference ; all the most highly-developed forms 

 of the " complex " type having been found near the surface, where 

 the temperature is the highest, and the supply of food most 

 abundant. But it can no more be said that these physical 

 agencies produced the advance, than that heat can viake a chick 

 out of the yolk and white of an egg, without a germ to appro- 

 priate and build up these materials. These physical agencies 

 supply only the conditions required for the evolutionary process, 

 — the source or spring of which is in the germ itself 



As Natural Selection gives no account of the changes in the 

 plan of groivth which constitute so marked a feature in the evo- 

 lutionary history of the Orbitolite, so, as it seems to me, it gives 

 no explanation of the appearance of nciv organs : the complete 

 possession of which fits their possessors for a higher condition of 

 existence, and accords with other modifications that enable them 

 to take advantage of it- but which, in their rudimentary state, 

 cannot be conceived to be of any service to animals altogether 

 framed upon a less advanced type, and continuing to live in 

 accordance with lower conditions. And I shall take, as a suitable 

 "instance," what is known as the "swimming bladder" of the 

 Fish, which is an earlier form of the organ that becomes a lung in 

 air-breathing Vertebrata. 



In the Vertebrate series we pass by a succession of stages from 

 the Fish, with gills fitted only for aquatic respiration, to the Reptile 

 which is fitted only for aerial respiration : the intermediate being 

 the true Amphibia, which, as regards their respiratory apparatus, 

 are fish in their early stage, and reptiles in the complete stage ; 

 some of them retaining their gills even after the development of 

 their lungs, so as to be able to live either in air or in water. 

 Now, the first rudiment of a "swimming bladder" that we meet 

 with in Fishes, is a little diverticulum or pouch opening off from 

 the pharynx or gullet ; and this extends itself in many cases so 

 as to become a bag or sac, lying along the spine, but entirely cut 

 off, by the closure of its neck, from any communication with the 



