28 Instinct and Intelligence 



Difflugia, one of the simplest of unicellular 

 beings, when it has reached its full size, pro- 

 trudes long pseudopodia which move over the 

 mud at the bottom of the water it inhabits, If 

 its pseudopodia come in contact with grains of 

 sand they contract with the sand adhering to 

 them, and pass it into their body^. These grains 

 of sand are subsequently employed as materials 

 to form a new shell for the Difflugia's offspring. 

 Professor Verworn, instead of grains of sand, 

 placed small fragments of coloured glass near 

 a Difflugia; some time afterwards he noticed a 

 heap of these fragments on the bottom of the 

 shell. He then saw a protrusion of protoplasm 

 issue from the shell in the shape of a new 

 Difflugia. Thereupon, the material collected by 

 the parent organism the fragments of coloured 

 glass were used to envelop the substance of 

 the young animal, and came to form a shell 

 similar to that enveloping the parent. Beha- 

 viour of this kind seems guided by instinct and 

 memory. 



Before leaving the Protozoa we may refer to 

 the Volvocinae, which appear to occupy an inter- 

 mediate position between unicellular and multi- 



