INSTINCTS 157 



former. Hormones produced by definite tissues, there- 

 fore, influence the instincts. We want to show that this 

 influence is due to a modification of tropistic reactions 

 by the hormones. 



Mating in certain fish, like Fundulus, consists in the 

 male pressing that part of its body which contains the 

 opening of the sperm duct against the corresponding part 

 of the female body. The latter responds by pressing back, 

 and the pressure of the body is maintained by both sexes 

 through motions of the tail. During this mutual pressure 

 or friction both sexes shed their sexual cells, sperm and 

 eggs, into the water, and since the openings of the cloaca 

 of the male and female, through which the sex cells are 

 shed, are brought almost in contact with each other, sperm 

 and eggs mix at the moment they are shed. This act of 

 mating is due to a stereotropism which exists only during 

 the spawning season and which is supposedly due to cer- 

 tain hormones existing at this time in the animal. The 

 existence of such hormones is also indicated by certain 

 colorations which develop and exist in the male during 

 this period. This stereotropism is to some extent specific 

 since it is exhibited by the contact between the two sexes. 

 The specificity of this stereotropism is of importance 

 and needs further experimental analysis, but that it is 

 in reality a type of common stereotropism is evidenced 

 by the fact that if during the spawning season we keep 

 females isolated from males in an aquarium the females 

 will go through the motions of mating and shed the eggs 

 every time they come in contact with the glass walls of the 

 aquarium. When they are kept permanently isolated from 

 the male they repeat this non-specific purely stereotropic 

 mating throughout the season. The eggs which they shed 

 they quite frequently devour. 



