118 HYPOTHESIS OF THE DEVELOPMENT OF 



'ander different conditions, as to both air and light. Oft 

 the contrary, we have seen reason for supposing that the 

 proportion of carbonic acid gas (the element fatal to ani- 

 mal life) was larger at the time of the carboniferous for- 

 mation than it afterwards became. We have also seen 

 that astronomers regard the zodiacal light as a residuum 

 of matter, enveloping the pun, and which was probably at 

 one time denser than it is now. Here we have the indi- 

 cations of causes for a progress in the purification of the 

 atmosphere and in the diffusion of light during the earlier 

 ages of the earth's history, with which the progress of or- 

 ganic life may have been conformable. An accession to 

 the proportion of oxygen, and the effulgence of the cen- 

 tral luminary, may have been the immediate prompting 

 cause of all those advances from species to species which 

 we have seen, upon other grounds, to be necessarily sup- 

 posed as having "taken place. And causes of the like na- 

 ture may well be supposed to operate on other spheres of 

 being, as well as on this. I do not indeed present these 

 ideas as furnishing the true explanation of the progress of 

 organic creation ; they are merely thrown out as hints to- 

 wards the formation of a just hypothesis, the completion 

 of which is only to be looked for when some considerable 

 advances shall have been made in the amount and charac- 

 ter of our stock of knowledge. 



Early in this century, M. Lamarck, a naturalist of the 

 highest character, suggested an hypothesis of organic pro- 

 gress which deservedly incurred much ridicule, although 

 it contained a glimmer of the truth. He surmised, and 

 endeavored with a great deal of ingenuity, to prove, that 

 one being advanced in the course of generations to ano- 

 ther, in consequence merely of its experience of wanta 

 calling for the exercise of its faculties in a particular di- 

 rection, by which exercise new developments of organs 

 took place, ending in variations sufficient to constitute a 

 new species. Thus he thought that a bird would be 

 driven by necessity to seek its food in the water, and that, 

 in its efforts to swim, the outstretching of its claws would 

 lead to the expansion of the intermediate membranes, and 

 it would thus become web-footed. Now it is possible 

 that wants and the exercise of faculties have entered in 

 some manner into the production of the phenomena 

 which we have been considering ; but certainly not in the 

 way suggested by Lamarck, whose whole notion fa obvi- 



