■154 ZOOLOGY 



it ceases (Fig. 411). If the temperature is too high, develop- 

 ment may be abnormal, so that a monstrosity is produced. 



Light has a less striking effect on the development of the 

 frog. If light is excludetl from the developing (^ggs, they will 

 develop more slo«4y. The acceleration of development Ijy 

 rather high temjierature and l^y daylight is probabl.y due 

 t(j a chemical effect of these agents. It indicates that devel- 

 opmiMit is a complex chemical process. 



Healing and Regeneration. — If the egg of a frog be ])ricked 

 slightly, there will be a loss of .substance, and the resulting 



Fig. 410. — Young tadpole of the frog. From Morgan, "Development 

 of the Frog's Egg." 



embryo will be at first aljnormal. Later, howe\'er, this abnor- 

 malitj^ will become smoothed over by appropriate ckn'elop- 

 ment. So, also, if the tail of the developing larva is mutilated, 

 the wound vail heal and the missing parts will be re-formed. 

 This capacity of the living organism to restore the normal 

 form after mutilation is seen also in man. For if some of the 

 skin l)e cut away, or even if parts of internal organs are removed 

 the wounds will n(it merelj' heal, but the lost part will regen- 

 erate. The remarkable thing is that in regeneration almost 

 exactly that is produced which was lost. Both regeneration 

 and healing in the adult are a survival of the same capacity for 

 development which we see in the egg. 



