98 APPENDIX. 



have indulged, are much to be regretted, for they have 

 been assumed from insufficient data, and can only be 

 regarded as shifting hypotheses, to be modified, con- 

 firmed, or rejected, with the progress of discovery. 

 The ingenious manner in which the shrewd author 

 of " The Vestiges " has brought these speculations to 

 bear in support of his own hypotheses, will, I trust, 

 prove a salutary caution. 



Organic Cells, p. 25. — In examining animal struc- 

 tures with the highest powers of the microscope, a 

 primogenial nucleated cell suddenly terminates our ana- 

 lysis, and forms the extreme limit of our power of in- 

 vestigation. Cells, therefore, appear to constitute the 

 minute and marvellous laboratory, in which the essen- 

 tial changes of organic life are performed; all the 

 various processes of vitality being effected by the agency 

 of cells, not distinguishable from each other by any 

 appreciable physical characters. Thus, one system of 

 cells secretes the bile, another the adipose substance, 

 another the nervous matter, and so forth; but how 

 these special products are formed by cells, apparently 

 of similar organisation, from the same nutrient fluids, 

 we know not. Whether the special endowment be- 

 longing to the system of cells of a particular organ, 

 depends on the intimate structure of the walls or tissue 



