424 OORRl KB. 



the germinating seed; the rate of each of th 



'ed by tlic temperature 1" uhich the 

 organism is subjected. Thus ova which arc ordin 

 hatched until tlic leaves suitable tor tlic food of their larvae 

 have been put forth, may be made, by artificial heal, to pro- 

 duce a brood in the winter ; whil>t, on the other hand, if they 

 be kept at a low temperature, their hatching may be 

 almost indefinitely without the destruction of their \itality. 

 The same is true, of i -tato ; and it it remarkable that 



during the latter part of that state, in which the <! :ital 



process goes on with extraordinary rapidity, there is in 

 :i insects a special ot' the 



perature of tlie embryo by a process resembling incuhut' 

 Whether, in addition to the heat imparted from without, there 

 is any addition of force developed with 



ing seed) by the return of a part of the oriranic constituents 

 of the food to the condition of binary compounds, cannot at 

 present be stated with confidence: the probability 



r. that such a retrograde metamorphosis does take pi 

 adequate evidence of its occurrence during tin- incubation of 

 the bird's e afforded by the liberation of carbonic 



1. which i> then- found to be an essential condition of the 

 developmental process. During the larva-state there is very 

 little power of maintaining an independent temperature, so 

 that the MiMeiiancc of vital activity is still mainly due to 

 the heat supplied from without. But in the active state of the 

 per t there is a production of heat quite comparable 



to that of warm-blooded animals ; and this is effected by the 

 retrograde metamorphosis of certain organic constituents of 

 the food, of which we find the expression in the exhalation of 

 carbonic acid and water. Thus the food of animals becomes 

 an internal source of heat, which may render them independ- 

 ent of external temperature. 



Further, a like retrograde metamorphosis of certain con- 

 stituents of the food is the source of that sensori-motor power 



