Chapter C: S. Minot, ‘Account, etc.;’ Proc. Boston Soc. Nat. Hist. vol. xix

p. 165, 1877.

Footnote 144:

E. van Beneden and Boveri have recently, quite independently of each
other, made a more exact study of these ‘Polkörperchen’
(‘Centrosoma,’ Boveri). They show that nuclear division starts from
these bodies, although the mode of origin of the latter is not yet
quite clear.—A. W., 1888.

Footnote 145:

The existence of polar bodies in sponges has been recently proved by
Fiedler: Zool., Anzeiger., Nov. 28, 1887.—A. W., 1888.

Footnote 146:

They have now been observed in many species, so that their general
occurrence in insects is tolerably certain. Compare bibliography
given in Weismann and Ischikawa, ‘Weitere Untersuchungen zum
Zahlengesetz der Richtungskörper,’ ‘Zoolog. Jahrbücher,’ vol. iii.
1888, p. 593.—A. W., 1888.

Footnote 147:

Van Beneden, even in his last work, considers these bodies to have
only the value of nuclei; l. c., p. 394.

Footnote 148:

I purposely abstain from using a more precise term, for the
complicated terminology employed in spermatogenesis hardly
contributes anything to the elucidation of the phenomena themselves.
Why do we not simply speak of sperm-cells and spermatoblasts, and
distinguish the latter by numbers when they occur in successive
generations of different form? Moreover, all the names which have
been suggested for successive stages of development, can only be
applied to the special group of animals upon which the observations
have been made. Hence great confusion results from the use of such
terms as spermatoblasts, spermatogonia, spermatomeres, spermatocysts,
spermatocytes, spermatogemmae, etc.

Footnote 149:

Fol, ‘Sur l’origine des cellules du follicule et de l’ovule chez les
Ascidies.’ Compt. rend., 28 mai, 1883.

Footnote 150:

Roule, ‘La structure de l’ovaire et la formation des œufs chez les
Phallusiadées.’ Ibid., 9 avril, 1883.

Footnote 151:

Balbiani, ‘Sur l’origine des cellules du follicule et du noyau
vitellin de l’œuf chez les Géophiles.’ Zool. Anzeiger, 1883, Nos.
155, 156.

Footnote 152:

Will, ‘Ueber die Entstehung des Dotters und der Epithelzellen bei den
Amphibien und Insecten.’ Ibid., 1884, Nos. 167, 168.

Footnote 153:

[It is almost certain that this vesicle is not derived from the
nucleus, but from the cytoplasm of the sperm-mother-cell. See Douglas
H. Campbell, ‘Zur Entwicklungsgeschichte der Spermatozoiden’ in
Berichte der deutschen botanischen Gesellschaft, vol. v, 1887, p.
122.—S. S.]

Footnote 154:

Bütschli, ‘Gedanken über die morphologische Bedeutung der sogenannten
Richtungskörperchen,’ Biolog. Centralblatt, Bd. VI. p. 5, 1884.

Footnote 155:

F. M. Balfour, ‘Comparative Embryology,’ vol. i. p. 63.

Footnote 156:

The formation of a polar body in parthenogenetic eggs has now been
proved: see note at the end of this Essay; see also Essay VI.—A. W.,
1888.

Footnote 157:

R. Leuckart,—article ‘Zeugung,’ in R. Wagner’s ‘Handwörterbuch der
Physiologie,’ 1853, Bd. IV. p. 958. Similar observations were made by
Max Schultze. These observations appear however to be erroneous, for
Pflüger has since shown that the eggs of frogs never develope if the
necessary precautions are taken to prevent the access of any
spermatozoa to the water.—A. W., 1888.

Footnote 158:

Oellacher, ‘Die Veränderungen des unbefruchteten Keims des
Hühncheneies. ‘Zeitschrift für wissenschaftliche Zoologie,’ Bd. XXII.
p. 181. 1872.

Footnote 159:

Hensen, ‘Centralblatt,’ 1869, No. 26.

Footnote 160:

Weismann, ‘Beiträge zur Naturgeschichte der Daphnoiden,’ Leipzig,
1876-79, Abhandlung VII, and ‘Zeitschrift für wissenschaftliche
Zoologie,’ Bd. XXXIII.

Footnote 161:

Weismann, ‘Beiträge zur Kenntniss der ersten Entwicklungsvorgänge im
Insectenei,’ Bonn, 1882, p. 106.

Footnote 162:

W. Roux, ‘Ueber die Bedeutung der Kerntheilungsfiguren.’ Leipzig,
1883.

Footnote 163:

We now know that the number of loops varies considerably in different
species, even when they belong to the same group of animals (e.g.
Nematodes).—A.W., 1888.

Footnote 164:

This expression is used by bee-keepers, for instance by the
well-known Baron Berlepsch. Of course, it would be more accurate to
say that the queen, seeing the cell of a drone, is stimulated to lay
an unfertilized egg, and that, on the other hand, she is stimulated
to lay a fertilized egg when she sees the cell of a worker, or that
of a queen.

Footnote 165:

E. Bessels, ‘Die Landois’sche Theorie widerlegt durch das
Experiment.’ Zeitschrift für wissenschaftliche Zoologie, Bd. XVIII.
p. 124. 1868.

Footnote 166:

‘Daphniden,’ Abhandlung, vi. p. 324.

Footnote 167:

l. c., p. 150.

Footnote 168:

Carl Düsing, ‘Die Regulirung des Geschlechtsverhältnisses.’ Jena.
1884.

Footnote 169:

I intend to publish these experiments elsewhere in connexion with
other observations.

Footnote 170:

Weismann, ‘Daphniden,’ Abhandlung, VII. p. 329; Herbert Spencer, ‘The
Principles of Biology,’ 1864, vol. i. pp. 229, 230.

Footnote 171:

The same fact has since been ascertained in species belonging to
several groups of animal.

Footnote 172:

Brooks, ‘The Law of Heredity.’ Baltimore, 1883, p. 73.

Footnote 173:

‘Zeitschrift für wissenschaftliche Zoologie,’ Bd. XXXIII. p. 107.
1873.

Footnote 174:

Valaoritis, l. c., p. 6.

Footnote 175:

I quote from Falkenberg, in Schenk’s ‘Handbuch der Botanik,’ Bd. II.
p. 219. He further states that these are the only instances hitherto
known in which undoubted male cells have proved to be capable of
further development when they have been unable to exercise their
powers of fertilization. It must be added that the two kinds of
germ-cells do not differ in appearance, but only in behaviour; the
female germ-cells becoming fixed, and withdrawing one of their two
flagella, while the male cells continue to swarm. But even this
slight degree of differentiation requires the supposition of internal
molecular differentiation.

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V.

THE SIGNIFICANCE OF SEXUAL REPRODUCTION
IN THE THEORY OF NATURAL SELECTION.

1886.

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SIGNIFICANCE OF SEXUAL REPRODUCTION, ETC.