30 Nature of the Formative Stimulus 
the zoospores which move about by means of their 
vibratile flagella and into which these mononuclear 
amoebae become transformed. And it is certain that 
phenomena likewise nervous in character must come into 
play when the cells of Magosphera planula become 
separated from one another and each one moves off 
independently by means of its cilia. 
One is justified then in suspecting that when these 
cells are united in a colony they may then also be the 
seat of phenomena of a nervous nature, and that the 
other ontogenetic stages of these minute organisms ought 
also to be attributed to such phenomena. 
But then we should have to refer the development of 
higher organisms also to phenomena of the same nature. 
As a support of this hypothesis we recall the well 
known fact that all cells of organisms, from these most 
primitive pluricellular forms up, are united to one another 
by a network of intercellular protoplasmic bridges. 
We recall the example which the different species of 
Volvox afford, a genus of lower algae consisting of a 
vesicle formed of a single layer of cells, very much like 
the blastula stage of the development of animals. All 
the species of Volvox show a perfectly typical and 
regular form of union between the different cells of the 
body. In Volvox aureus for example, the superficial 
cells of the trophic hemisphere of the vesicle lie in a thick 
soft gelatinous mucus and each is not only provided with 
two long flagellae, but also is connected with each of 
the five or six adjoining cells by a long, thin protoplasmic 
filament. In the germinal hemisphere the protoplasmic 
filaments are more numerous so that each of the great 
spores which arise there is connected with each one of 
the large neighboring cells by bundles of from three to 
