132 Prof. B. Forbes on the supposed Analogy between the 



mencement, and each has its cessation. Geological research 

 has made known to us that prior to certain points in time 

 certain species did not exist, and that after certain points in 

 time certain species ceased to be. The commencement of a 

 species has been compared with Birth, the extinction with 

 Death. Again, many species can be shewn to have had an 

 epoch of maximum development in time. This has been 

 compared with the maturity of the individual. 



Between the birth of an individual and the commencement 

 of a species in the first appearance of its protoplast, the ana- 

 logy is more apparent than real. We know how the former 

 phenomenon takes place, but we have no knowledge of the 

 latter. 



Between the maturity of the individual and the maximum 

 development of a species there is no true analogy, since the 

 latter can easily be proved to be entirely dependent on the 

 combination of favouring conditions, and during the period 

 of duration of a species there may be two or more epochs of 

 great or even equal development, and two or more epochs of 

 decline alternating with epochs of prosperity. The epoch of 

 maximum of a species may also occur during any period in 

 its history short of the first stage. Geological and geogra- 

 phical research equally shew that the flourishing of a species 

 is invariably coincident with the presence of favouring, and 

 its decline with that of unfavourable conditions. Hence there 

 is no analogy between the single and definite phase of ma- 

 turity of the individual and the variable and sometimes often 

 repeated epochs of luxuriant development in the duration of 

 a species. 



Between the death of the individual and the extinction of 

 a species there is an analogy only when the former event 

 occurs prematurely, through the influence of destroying con- 

 ditions. But in their absence, an individual after its period 

 of vitality has been completed must necessarily die ; whereas 

 we have no right to assume that such would be the fate of a 

 species so circumstanced, since in every case where we can, 

 either geologically or geographically, trace a species to its 

 local or general extinction, we can connect the fact of its 

 disappearance with the evidences of physical changes. 



