[20] The same difference was found in this form in regard to heliotropism. [21] Palæmon and Sicyonia. [22] The regeneration of the lens of triton may also be affected by gravity. [23] Driesch does not give in his paper (’99) the position of the hydroids, or the method of the experiment, but I can supply the details given above from a personal communication from Driesch. [24] Jacobson has shown that the layer of water just above the sedimentary layer at the bottom is poor in oxygen. [25] “There is thus _manifested in the formative force of the tubularia-stem a well-marked polarity_, which is rendered very apparent if a segment be cut out from the centre of the stem.” Allman (’64). [26] The same holds good for the basal hydranth if it arises near an oblique end. [27] Although it is by no means certain that the results may not be due in part, at least, to injuries to the nervous system. [28] In normal animals some have the right claw the larger and some the left. [29] In other plants, fumaria, for example, non-nucleated pieces do not seem to be able to make new starch after using up that which they contain at first. [30] I have found that the closing in takes place equally well when one per cent of KCl is added to the sea water. This salt has, as Loeb has shown, an inhibiting effect on muscular contractility,--not, however, on amœboid movements. [31] Knight obtained similar results in 1809. [32] Vöchting points out that a parallel case is found in certain conifers. In these there arise from a vertical many-sided main stem whorls of side branches that are symmetrical in one plane. These lateral branches, if cut off and planted, produce new roots and new branches, but the latter are always side-branches, like the parts from which they arise. They never produce a normal main axis. Nevertheless, although these branches cannot themselves produce a main shoot, a callus may be formed at the base of the piece, and from this a new main stem may arise. [33] A piece suspended in ordinary air dries up without producing any new structures. [34] Goebel, ’98, page 37. [35] Examples of this are found in _Lilium candidum_, _Lachenalia luteola_. [36] Delage and Giard give Lessona (’69) the credit for first stating that the phenomenon of regeneration is an adaptation to liability to injury; but Réaumur first suggested this idea in 1742, and Bonnet in 1745. Delage’s interpretation, viz. that Lessona ascribed this to a _prévoyance de la nature_, has been denied by Lessona’s biographer, Camerano (_La Vita di M. Lessona_, _Acad. R. d. Torino_, 2, XLV, 1896), and by Giard (_Sur L’autotomie Parasitaire_, etc., _Compt. Rendus de Séances de la Société de Biologie_, May, 1897). [37] Whether, having once failed in this way to obtain the snail, the bird or lizard would not learn to make a frontal attack is not stated. Or shall we assume that the tail is all that is wanted? [38] _The Germ Plasm._ Translation by W. Newton-Parker, 1893, page 116.