114 THE BRAIN OF THE TIGER SALAMANDER 



ancestors. Such reversals and the accompanying instances of actual 

 degeneration doubtless are brought into being by changes in the 

 mechanism of heredity, involving rearrangement of the complicated 

 pattern of the genes (Emerson, '42, '45). Evolution is an irreversible 

 process, with divergent ramifications in inconceivable variety and 

 many instances of approximate parallelism. The apparent repeti- 

 tions, when viewed in time, are not circular but spiral in form; and 

 apparent retrogressions are never exact reversals of the preceding 

 historical sequence. When a mammal returns to the water, it does not 

 become a fish. The amphibians present conspicuous illustrations of 

 recapitulation in individual development of some features of the 

 phylogenetic history, and most of the apparent retrogression is really 

 an arrest of development, which does not go back so far as the piscine 

 ancestry. Their limbs are not fins, and their gills are not fishlike. 

 There is another functional factor in morphogenesis to which too 

 little attention has been given— a greater or less capacity for so- 

 called "spontaneous" activity, that is, behavior initiated internally 

 and manifested in patterns determined by the intrinsic structure. 

 All protoplasm is active as long as it is alive, and the essential vital 

 properties are inherent in protoplasmic organization. This behavior 

 is not a mere reflection of external influences, for the living stuff 

 transforms the energies which impinge upon it and recombines them 

 in original designs. Reserves are accumulated, and these are ex- 

 pendable on occasion in accordance with need, with or without ex- 

 ternal excitation. In the central nervous system this intrinsic "spon- 

 taneous" automaticity attains maximum potency, and it is exhibited 

 by even isolated fragments of it in characteristic patterns, of which 

 oscillographic records can be made. In the intact brain the interplay 

 of these intrinsic activities is always going on, and as we pass from 

 lower to higher animal types it becomes progressively a more and 

 more important factor in determining patterns of behavior. The 

 enormous reserves of potential nervous energy in the brain are 

 evoked and manifested as stabilizing influences (cerebellum, corpus 

 striatum, etc.) and also in that spontaneity, initiative, and inventive- 

 ness which culminate in cortically directed human behavior. These 

 capacities are shown in some measure by all animals, and a search for 

 the apparatus employed in even so lowly a creature as a salamander 

 may be fruitful (see '48, chap, xv, for discussion of Coghill's con- 

 tributions on automatism, spontaneity, and motivation). 



