PREFACE. VII 



casing the mother. These fragments of glass, loosely interjoined 

 at first, were now cemented together by a substance secreted by 

 the body of the animal. 



Two facts are to be remarked in this observation: first, the act 

 whereby the Diffiugia collects the materials for providing the young 

 individual with a case, is an act of preadaptation to an end not 

 present, but remote; this act, therefore, has all the marks of an 

 instinct.^ Further, the instinct of the Difflugia exhibits great pre- 

 cision; for the Difflugia not only knows how to distinguish, at the 

 bottom of the water, the materials available for its purpose, but it 

 takes only the quantity of material necessary to enable the young 

 individual to acquire a well-built case; there is never an excess. 



It is interesting to note that the Diffiugia does not act differ- 

 ently from animals possessing more highly complicated organiza- 

 tions and endowed with differentiated nervous systems, as for in- 

 stance, the larvas of Phryganids which form their sheaths from 

 shells, grains of sand, or minute slivers. 



We shall not regard it as strange, perhaps, to find so complete 

 a psychology in the history of lower organisms, when we call to 

 mind that, agreeably to the ideas of evolution now accepted, a higher 

 animal is nothing more than a colony of protozoans. Every one of 

 the cells composing such an animal, has retained its primitive proper- 

 ties, giving them a higher degree of perfection by division of labor 

 and by selection. The epithelial cells that secrete the nails and the 

 hair are organisms perfected with reference to the secretion of 

 protective parts. Similarly, the cells of the brain are organisms 

 that have been perfected with reference to psychical attributes. 



Paris, November 20, 1888. 



Alfred Binet. 



