[75] Müller, Elements of Physiology, 1837.
[76] By Wagner (’87).
[77] For references to the literature on grafting in plants see Vöchting (’84).
[78] In one case they separated only after three months.
[79] This and other experiments were carried out by pushing the pieces on a bristle.
[80] Rand found that when a posterior piece was grafted by its cut, oral end to the side of another hydra that it was absorbed into the stock. In one case it moved down the whole length of the body of the stock and finally disappeared by absorption into the foot of the stock.
[81] Pieces from male and female colonies of the same species also unite.
[83] It is not certain whether this is a head or a tail.
[84] Joest states that this new part is a head, as shown by the presence of food matter in the digestive tract of the posterior piece.