[305] As I have been unable to obtain a copy of the _Introduction_, the passages which follow are taken from the _Rapport_ of 1867, where Milne-Edwards gives a complete exposition of his doctrine, sometimes in the words of the original. [306] This principle was first developed by Milne-Edwards in 1827, in the _Dictionnaire classique d'Hist. naturelle_. It was probably suggested to him by his studies on the Crustacea, among which the principle is so beautifully exemplified in the concentration and specialisation of the appendages and the ganglionic chain. [307] Studied by Isidore Geoffroy St Hilaire in his paper _Classification parallelique des Mammiferes, C. R. Acad. Sci._, xx., 1845. Remarked upon by Cuvier, _Regne animal_., i., p. 171, 1817, also by de Blainville. [308] Cuvier et Valenciennes, _Hist. nat. des Poissons_, i., p. 550, 1828. [309] _Myxinoiden_, Th. I. _Abh. k. Akad. Wiss. Berlin_ for 1834, pp. 100, 110, 179, etc. [310] _Vergl. Entw. Kopf. nackt. Amphibien_, p. 101, 1838. [311] I have not seen the companion volume on palaeontological progression, _Unters. ue. d. Entwickelungsgesetze der organischen Welt waehrend der Bildungszeit unserer Erdoberflaeche_, Stuttgart, 1858. [312] "Strobiloid" because of its spiral development. The theory of the spiral growth of plants played an important part in botanical morphology about this time. [313] _Cf._ Meckel's Principle of progressive Evolution, _supra_, p. 93. [314] _System der thierischen Morphologie_, pp. 33, 457. Also C. Bruch, _Die Wirbeltheorie des Schaedels, am Skelette des Lachses geprueft_, Frankfort-on-Main, 1862. [315] In France the vertebral theory was advocated by Lavocat in his _Nouvelle Osteologie comparee de la tete des animaux domestiques_, Toulouse, 1864. It seems also that Lacaze-Duthiers held fast to it even in 1872--_Arch. zool. exp. gen._, i., p. 51, 1872. [316] _An Essay on Classification_, Boston, 1857, London, 1859. He considered the classificatory categories to be the categories of the Creator's thought, and hence natural, and in no sense mere conventions. [317] "Principes d'Embryogenie, de Zoogenie et de Teratogenie," _Mem. Acad. Sci._, xxv., pp. 1-943, pls. xxv., 1860. [318] "On the Morphology of the Cephalous Mollusca," _Phil. Trans._, 1853, _Sci. Memoirs_, i., pp. 152-92. [319] "Observations sur les changements de forme que les divers Crustaces eprouvent," _Ann. Sci. nat._ (1) xxx., p. 360, 1833. [320] "Considerations sur quelques principes relatifs a la classification naturelle des animaux," _Ann. Sci. nat._ (3) i., p. 65, 1844. [321] _Supra_, pp. 79-83. Also _Precis d'anatomie transcendante, principes d'organogenie_, Paris, 1842.