130 CALIFORNIA ACADEMY OF SCIENCES. 



iiig the territory occupied by a species into two or more 

 sections." 



(d) 9. Fertilizational Segregation. Repugnance of 

 insects to visiting different plants interchangeably pre- 

 vents hybridization. 



(e) Artificial Segregation. Artificial selection. 



B. Reflexive Segregation. " Segregation arising 

 from the relations in which the members of one species 

 stand to each other." 



(a) Conj agational Segregation. Due to "the in- 

 stincts by which organisms seek each other and hold 

 together in more or less compact communities." 



10. Social. " Produced by the discriminative action 

 of social instincts. The law of social instinct is prefer- 

 ence for that which is familiar in one's companions; 

 and, as in most cases the greatest familiarity is gained 

 with those that are near of kin, it tends to produce 

 breeding within the clan," etc. 



11. Sexual. " Produced by the discriminative action 

 of sexual instincts." 



12. Germinal. "Caused by the propagation of the 

 species by means of seeds or germs any one of which, 

 when developed, forms a community so related that the 

 members breed with each other more frequently than 

 with the members of other communities." 



13. Floral. Self-fertilization of flowers. 



(b) Impregnational Segregation. Physiological se- 

 lection par excellence. 



14. Segregate Size. Inability of varieties to inter- 

 breed, owing to difference in size. 



15. Segregate Structure. Due to "lack of correla- 

 tion in the proportionate size of different organs, and 

 by other incompatibilities of structure." 



16. Potential and Prepotential. "Caused by more 

 or less free distribution of the fertilizing element to- 



