2. The tubular structures have fibrillar walls that may be covered, eventually, by a membranous layer of leukocytes. Their lumina contain blood cells suspended in fluid.

3. The formation of the tubules is initiated by the red cells. The leukocytes, and more particularly the thrombocytes, are responsible for the construction of the walls.

4. The phenomenon occurs only in the presence of plasma, the coagulation of which has been slightly delayed. Once the surrounding medium has become firmly coagulated, no further change occurs either in the length of the tubules or in their diameter.

5. The development of the tubules is not suppressed by substances that enhance cellular activity unless they induce, at the same time, the immediate coagulation of the medium. The addition of embryo tissue juice prevents their formation by producing early coagulation.

6. The phenomenon as a whole is dependent upon the physicochemical nature of the medium, the character and thickness of the explanted fragment, and the physical and physiological peculiarities of the cells that comprise it. It is the expression of various physicochemical and physiological events that have occurred in a definite order, or sequence.