working on the egg of _Dentalium_. He found that if the similar anucleate "polar lobe" of this form is removed at the two-celled stage, deficient larvae are formed, in which the post-trochal region and the apical organ are absent. He further showed that in the unsegmented but mature egg prelocalised cytoplasmic regions can be distinguished, which later become separated from one another through the segmentation of the egg. The segmentation-cells into which these cytoplasmic substances are thus segregated show a marked specificity of development, giving rise, even when isolated, to definite organs of the embryo. Wilson concluded that the cytoplasm of the egg contains a number of specific organ-forming stuffs, which have a definite topographical arrangement in the egg. Development is thus due in part to a qualitative division not of the nucleus but of the cytoplasm. Corroborative evidence of the existence of cytoplasmic organ-forming stuffs has been supplied for several other species, _e.g._, _Patella_ (Wilson), _Cynthia_ (Conklin), _Cerebratulus_ (Zeleny), and _Echinus_ (Boveri).

It is interesting to recall that so long ago as 1874 W. His[504] put forward the theory that there exist in the blastoderm and even in the egg prelocalised areas, which contain the formative material for each organ of the embryo, and from which the embryo is developed by a simple process of unequal growth.

The experimental study of form was prosecuted in many other directions besides that of experimental embryology. The study of regeneration and of regulatory processes attracted many workers, among whom may be mentioned T. H. Morgan, C. M. Child, and H. Driesch. In an interesting series of papers C. Herbst applied the principles of the physiology of stimulus to the interpretation of development.[505] The formative power of function was studied in Germany by Roux and his pupils, Fuld, O. Levy, Schepelmann and others, particularly by E. Babak. In France, F. Houssay inaugurated[506] an important series of memoirs by himself and his pupils on "dynamical morphology," the most important memoir being his own valuable discussion of the functional significance of form in fishes.[507]

The principles of his dynamical morphology were first laid down in his book _La Forme et la Vie_ (1900).

The famous experiments of Loeb, Delage and others on artificial parthenogenesis may also be mentioned, though their connection with morphology is somewhat remote.

The period was characterised also by the lively discussion of first principles, in which Driesch took a leading part. Materialistic methods of interpretation were upheld by perhaps the majority of biologists, but vitalism found powerful support.

[464] See Carus's remark, referred to on p. 194, above.

[465] Roux, _Die Entwicklungsmechanik_, p. 26, Leipzig, 1905.

[466] T. H. Morgan, _Regeneration_, p. 1, New York and London, 1901.

[467] _Recherches sur la production artificielle des Monstruosites_, Paris, 1877, and many later papers.

[468] _Unsere Korperform und das physiologische Problem ihrer Entstehung_, Leipzig, 1874.

[469] J. W. Jenkinson, _Experimental Embryology_, p. 3, Oxford, 1909.

[470] "Ueber die Verzweigungen der Blutgefa.s.se des Menschen," _Jen. Zeit_., xii., 1878.

[471] "Ueber die Bedeutung der Ablenkung des Arterienstammes bei der Astabgabe," _Jen. Zeit_., xiii., 1879.

[472] "Beitrage zur Morphologie der funktionellen Anpa.s.sung. I. Struktur eines hochdifferenzierten bindgewebigen Organes (der Schwanzflosse des Delphin),"

_Arch. Anat. Physiol._ (_Anat. Abt._) for 1883. II.

"Ueber die Selbstregulation der 'morphologischen' Lange der Skeletmuskeln des Menschen," _Jen. Zeit._, xvi., 1883. III. "Beschreibung ... einer Kniegelenkeknochenankylose," _Arch. Anat. Physiol._ (_Anat. Abt._) for 1885.

[473] In 1869 and 1877 respectively (Roux, p. 53, 1905).

[474] _Ueber die Zeit. der Bestimmung der Hauptrichtungen des Froschembryo_, Leipzig, 1883.

[475] "Ueber den Einfluss der Schwerkraft auf die Teilung der Zellen," Pfluger's _Archiv_, x.x.xi., 1883. Also subsequent papers in same journal.

[476] For an account of the cla.s.sical experiments on the frog's egg, see T. H. Morgan, _The Development of the Frog's Egg_, New York, 1897.

[477] In a series of "Beitrage zur Entwicklungsmechanik des Embryo," published in various journals from 1884 to 1891, all dealing with the frog's egg. Also in many papers in the _Archiv f. Entw. mech._, from 1895 onwards.

[478] _Die Entwicklungsmechanik der Organismen, eine anatomische Wissenschaft der Zukunft_, Wien, 1890.

[479] The first volume contains the important _Einleitung_ or general Introduction.

[480] _Gesammelte Abhandlungen uber Entwicklungsmechanik der Organismen_, 2 vols., Leipzig, 1895.

[481] "Fur unser Programm und seine Verwirklichung,"

_A.E.M._, v., pp. 1-80 and 219-342, 1897. "Ueber die Selbstregulation der Lebewesen," _A.E.M._, xiii., pp.

610-5, 1902. "Die Entwicklungsmechanik, ein neuer Zweig der biologischen Wissenschaft," Heft I. of the _Vortrage u. Aufsatze uber Entwicklungsmechanik der Organismen_, Leipzig, 1905. Oppel and Roux, "Ueber die gestaltliche Anpa.s.sung der Blutgefa.s.se," Heft x., of the _Vortrage u.

Aufsatze_, Leipzig, 1910.

[482] "Ueber d. funkt. Anpa.s.sung des Muskelmagens der Gans," _A.E.M._, xxi., pp. 461-99, 1906.

[483] The exact quant.i.tative formulation of a _Wirkungsweise_ const.i.tutes a law. The word itself is perhaps most conveniently rendered as "causal process."

[484] M. Furbringer, perhaps under the influence of Roux, emphasised the importance, from a morphological point of view, of studying post-embryonic (functional) development, _Unters. z. Morph. u. Syst. der Vogel_, ii., Amsterdam, p. 925, 1888.

[485] See, for the development of this idea, Oppel, in Roux-Oppel, 1910.

[486] _Cf._ the controversy between Herbert Spencer and Weismann on the subject of "coadaptation" in the _Contemporary Review_ for 1893 and 1894. See also Weismann's paper in _Darwin and Modern Science_, Cambridge, 1909.

[487] That is, the length they take up when separated from the body.

[488] "Wilhelm Roux zum 60. Geburtstage," _Arch. f.

Entw.-Mech._, x.x.x. _Festschrift fur Prof. Roux_, Pt. i, 1910.

[489] Virchow's _Archiv_, cxiv., 1888. First announced in Sept. 1887.

[490] _Ueber die Bedeutung der Kernteilungsfiguren_, Leipzig, 1883.

[491] _Bresl. artz. Zeitschr._, 1885.

[492] _Journ. de l'Anat. et de la Physiologie_, xxiii., 1887.

[493] _Zeits. f. wiss. Zool._, liii., 1891 and 1892.

[494] _Journ. Morph._, viii., 1893.

[495] _Arch. f. Ent.-Mech._, i., 1895; ii., 1896.

[496] _Arch. f. mikr. Anat._, xliii., 1893.

[497] _Arch. f. Ent.-Mech._, iii., 1896.

[498] _Arch. f. Ent.-Mech._, i., 1895.

[499] _Anat. Anz._, x., 1895.

[500] _Arch. f. Ent.-Mech._, iv. 1897.

[501] _Arch. f. Ent.-Mech._, ii., 1896.

[502] _Arch. f. Ent.-Mech._, iii., 1896.

[503] _Journ. exper. Zool._, i., 1904.

[504] _Unsere Korperform_, p. 19, Leipzig, 1874.

[505] _Biolog. Centrlbl._, xiv., 1894, xv., 1895.