60 HEREDITY AND ENVIRONMENT 



nections are formed, the protoplasm of the 

 muscle cells probably responding directly to 

 the chemical stimulus of certain salts in the 

 body fluids, as Loeb has shown in other cases. 

 Reflexes which appear later are the random 

 movements of the voluntary muscles of limbs 

 and body, which are called forth by nerve im- 

 pulses. Tropisms are manifested only by or- 

 ganisms capable of considerable free movement 

 and hence are absent in the foetus though 

 present in many free living larva?. Some in- 

 stincts are present immediately after birth, 

 such as the instinct of sucking or crying, 

 though these are so simple when compared 

 with some instincts which develop later that 

 they might be classed as reflexes ; it is doubtful 

 whether any of the activities before birth could 

 properly be designated as instincts. Reflexes, 

 tropisms and instincts have had a phylogenetic 

 as well as an ontogenetic origin, and conse- 

 quently we might expect that they would in 

 general make for the preservation of the 

 species, and as a matter of fact we usually find 

 that they are remarkably adapted to this end. 

 For instance the instincts of the human infant 



