Vice-Fresidenfs Address. 281 



also to trace their fossil predecessors throughout a long 

 series of geological periods from the dawn of life on the 

 globe down to the present day. When a common ancestor 

 to two or more present-day species is disinterred, we have to 

 carry our imagination back to the time when it was an 

 individual member of a living species, similarly affiliated 

 to pre-existing predecessors — for however distant the rela- 

 tionship of a fossil may be from its present representatives, 

 whether it be regarded as a genus, family, or order, the 

 day was when it flourished as a species. By continuing 

 this line of investigation backwards in time, through the 

 successive sedimentary strata which form the larger portion 

 of the earth's crust, we gradually encounter less and less 

 specialised forms, till ultimately the most divergent types 

 meet in a common origin among unicellular organisms, 

 analogous to those still prevalent on the borderland of 

 the animal and vegetable kingdoms, such as the amoeba, 

 red-snow plant, yeast, etc. 



Another important generalisation, which has been demon- 

 strated by the dissection of animals, is that, however dissimilar 

 living forms may appear, they are structurally but a congeries 

 of unicellular organisms grouped together on a uniform plan, 

 and working in the animal economy on the principle of the 

 division of labour. Now, many of these lower organisms 

 exhibit, though, of course, in a most rudimentary manner, 

 nearly all the vital phenomena of the higher animals — 

 voluntary motion, assimilation of food, growth and main- 

 tenance, reproduction, decay and death. The human body 

 may thus be regarded as a combination of groups of amcebce, 

 so arranged as to subordinate their original individualism 

 to the general welfare of the compound organism. In the 

 course of long ages these cell units have become adapted 

 in various ways for their special work by entering into 

 the structure of the animal's tissues, or floating about as 

 corpuscles in blood and secretions. Thus they build up 

 cellular membrane, muscular fibre, medullary matter, brain 

 cells, etc., by means of which all the animal functions are 

 performed from simple molecular movements up to conscious 

 cerebration. The theory, first propounded by Schwann about 



