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. 17 



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 



16 Adam Sedgwick: The Development of the Cape Species of 

 Peripatus. Quart. Journ. of microscopical Science. XXVI, 1886. P. 

 198200, 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 ina 

 tierischen Organismus. From the Sitzungsberichten der Phys.-Med. 

 Gesellschaft zu Wurzburg. Sitzung vorn Febr. 25, 1893; P. I 8. 



