270 BIOLOGICAL LECTURES. 



vidual itself, and that reproduction is merely a means of enabling 

 this individual to undergo a greater change in form, to become 

 an individual of a different kind. Something similar to gener- 

 ation is seen when maggots become flies and caterpillars butter- 

 flies." At another place, in the " Theodicee," he says, 1 after 

 referring to the microscopic observations of Leeuwenhoek : 

 " Thus I would contend, that the souls, which are some day to 

 become human souls, were already present in the germ like 

 the soiils of other species, that they have always existed in our 

 fore-fathers as far back as Adam, i.e., since the beginning 

 of things, in the form of organized bodies." These remarks 

 of Leibnitz are the ne plus ultra formulation of the theory of 

 emboitement its extension to embrace not only the physical 

 but also the psychical and spiritual aspect of living things. 



It is, perhaps, easy to understand how philosophical and 

 religious preconceptions could give this final form to the theory 

 of emboitement. Other considerations, however, of a more 

 real and scientific character seem to have led men's minds in 

 the same directions. The microscope, invented in the six- 

 teenth and bequeathed to the seventeenth century, had pro- 

 foundly influenced speculation. Magnification had revealed, 

 as if by magic, the existence of a great world of structures 

 undreamed of by the greatest intellects the race had hitherto 

 produced. The authority of the ancients weakened perceptibly, 

 for little value could thenceforth be attached to their opinions 

 on the nature of the great world that stretched out beyond the 

 confines of unaided vision. The mind, full of the great micro- 

 scopic discoveries of the time, was carried away by its own 

 inertia, and, outrunning the instrument, first dreamed of and 

 then believed in the existence of structures too minute to be 

 revealed by the available lenses. This speculation was, per- 

 haps, justifiable, except when it undertook to define the pre- 

 cise nature of what was at that time an ultra-microscopic region. 

 It was natural but erroneous to conceive unseen structures as 

 diminutive duplicates of the seen. The verisimilitude of this 

 error increased when it became apparent that the microscope 

 was unable to resolve perfectly transparent structures even of 



i Op. Phil., p. 527. 



