40 Nature of the Formative Stimulus 
separated but remain connected by protoplasmic fila- 
ments; the cells which arise from each of the first two 
cells are associated in the same manner, and this con- 
tinues indefinitely. So that during the whole of develop- 
ment from the first segmentation of the egg up to the 
adult stage all the cells of the organism remain in inter- 
communication by means of these protoplasmic bridges. 
“The connection of cell with cell is not a secondary 
feature acquired late in development, but is primary 
dating from the very beginning of development.” 16 
It is quite unnecessary to recall the universality of 
intercellular bridges not only between the cells of each 
tissue but also between the cells of different tissues: 
between the epithelial cells of gland ducts and contiguous 
smooth muscle cells, between epithelial cells and con- 
nective tissue cells, between connective tissue cells and 
endothelial cells, between smooth muscle cells and con- 
nective tissue cells, between connective tissue cells and 
striated muscle fibers, between striated muscle fibers and 
epithelial cells, and so on.’” 
It is necessary to be remarked further that in animals 
this circulation of nervous currents can and at least in 
certain stages of development must certainly utilize 
not only the protoplasmic network uniting the cells to 
1®Adam Sedgwick: The Development of the Cape Species of 
Peripatus. Quart. Journ. of microscopical Science. XXVI, 1886. P. 
198—200, 206. 
"See for instance: Heidenhain: Uber das Vorkommen von 
Interzellularbriicken zwischen glatten Muskelzellen und Epithelzellen 
des ausseren Keimblattes und deren theoretische Bedeutung. Anat. 
Anzeiger, VIII, No. 12 and 13; May 13, 1893; P. 404—410; and 
Schuberg: Uber den Zusammenhang verschiedener Gewebezellen im 
tierischen Organismus. From the Sitzungsberichten der Phys.-Med. 
Gesellschaft zu Wiirzburg. Sitzung vom Febr. 25, 1893; P. 1-8 
