VITAL FORCE. 277 



with the appearance of the tadpole of the frog, 

 and triton, and the birth of the lamb : we might 

 compare the progress of the expanding bud or 

 bulb with "that of the ova, those of birds 

 for example, each kind of which has its deve- 

 loping period ; thus the time of incubation of 

 the barn-door fowl is as near as possible three 

 weeks; of the common duck, a month; of the 

 goose, five weeks ; of the swan, six weeks. I 

 need not specify analog6us examples of the 

 opening of the leaves of several trees, or the 

 flowering of the bulbs of several plants. 



AMICUS. It is a good subject for reflection, 

 and surely for admiration, seeing how that 

 which appears to be the regulating influence is 

 co-ordinate in its various degrees, from just 

 above the freezing point of water to the highest 

 average heat of the tropics, with distinct species 

 of animals and vegetables, securing to the whole 

 of our globe at its surface animal and vegetable 

 life, and for most part with a profuse bounty. 



PISCATOR. Yes, the external temperature is 

 so co-ordinate, as you remark, with the plants 

 and the families of the lower animals, mainly 

 the oviparous not so much so with the vivi- 

 parous, and of these least of all with the highest 



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