ef even in 1877.[282] Though Barry had held in 1839 that
the egg-nucleus does not disappear in segmentation, J. Mueller seems to
have been the first actually to prove that it forms by division the
nuclei of the first two segmentation spheres. He furnished the
demonstration in the egg of _Entoconcha mirabilis_,[283] and his paper was
known to Remak, who could not, however, observe a similar division of
the egg-nucleus in the frog. Mueller's discovery was confirmed for
_Oceania armata_ by Gegenbaur,[284] and for _Notommata sieboldii_ by
Leydig.[285]

In 1854 Virchow,[286] previously a supporter of Schwann, crystallised the
new views in the famous phrase--_Omnis cellula e cellula_--and gave wide
publicity to them in his classical lectures on Cellular Pathology,
delivered in 1858.[287] The new doctrine of cell-formation was also taught
by Leydig[7] in his text-book of histology, published in 1857.

The Schleiden-Schwann theory of the origin of cells by generation in a
cytoblastem was now definitely overthrown.

The importance of the protoplasmic content of the cell was brought into
prominence through the work of Dujardin,[289] Purkinje,[290] Cohen[291] and
Max Schultze.[292] The last-named in 1861 proposed a definition of the
cell which might be accepted at the present day. "A cell," he wrote, "is
a little blob of protoplasm containing a nucleus" (p. 11).

[238] _Theoria generationis_, Halae, 1759.

[239] See J. v. Sachs, _Geschichte der Botanik_, book ii.,
Eng. Trans., 2nd impr., 1906.

[240] Mueller's _Archiv_, pp. 137-76, 1838.

[241] _Trans. Linnean Soc._, xvi., p. 710, 1833.

[242] _Myxinoiden_, i. Theil., p. 89, 1835.

[243] _Ann. Sci. nat._ (2) (_Zool._) ii., pp. 107-18, pl.
11, 1834.

[244] _Proc. Phil. Soc. Glasgow_, xix., pp. 71-125,
1887-8.

[245] _Traite sur le venin de la vipere_, 1781.

[246] Mueller's _Archiv_, 1836.

[247] J. Mueller, _Jahresbericht ue. d. Fortschritte der
anat.-physiol. Wissenschaften im Jahre_ 1838. Mueller's
_Archiv_, 1838.

[248] _Symbolae ad anatomiam villorum imprimis eorum
epithelii_, Berlin, 1837.

[249] _U. d. Ausbreitung des Epitheliums im menschlichen
Koerper_. Mueller's _Archiv_, 1838.

[250] See Schwann's _Bemerkungen_ at the end of his
_Mikroskopische Untersuchungen_.

[251] Republished in Ostwald's _Klassiker der exakten
Wissenschaften_, No. 176, Leipzig, 1910. Re