[54] See some good criticisms on this head by Delpino and by Mr. G. H. Lewes in the ‘Fortnightly Review,’ Nov. 1st, 1868, p. 509.
[55] Mr. Herbert Spencer (‘Principles of Biology,’ vol. ii., p. 430) has fully discussed this antagonism.
[56] The male salmon is known to breed at a very early age. The Triton and Siredon, whilst retaining their larval branchiæ, according to Filippi and Duméril (‘Annals and Mag. of Nat. Hist.,’ 3rd series, 1866, p. 157) are capable of reproduction. Ernst Haeckel has recently (‘Monatsbericht Akad. Wiss. Berlin,’ Feb. 2nd, 1865) observed the surprising case of a medusa, with its reproductive organs active, which produces by budding a widely different form of medusa; and this latter also has the power of sexual reproduction. Krohn has shown (‘Annals and Mag. of Nat. Hist.,’ 3rd series, vol. xix., 1862, p. 6) that certain other medusæ, whilst sexually mature, propagate by gemmæ. See also Kolliker, ‘Morphologie und Entwickelungsgeschichte des Pennatulidenstammes,’ 1872, p. 12.
[57] See his excellent discussion on this subject in ‘Nouvelles Archives du Museum,’ tom. i., p. 151.
[58] ‘Proc. Boston Soc. of Nat. Hist.,’ republished in ‘Scientific Opinion,’ Nov. 10th, 1869, p. 488.
[59] Todd’s ‘Cyclop. of Anat. and Phys.,’ vol. iv., 1849-52, p. 975.
[60] ‘Compte Rendus,’ Nov. 14th, 1865, p. 800.
[61] As previously remarked by Quatrefages, in his ‘Métamorphoses de l’Homme,’ etc., 1862, p. 129.
[62] Günther’s ‘Zoological Record,’ 1864, p. 279.
[63] Sedgwick, ‘Medico-Chirurg. Review,’ April 1863, p. 454.