Essays Upon Heredity and Kindred Biological Problems

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.

147

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

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.

149

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

150

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

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.

152

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

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.]

154

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

155

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

156

The formation of a polar body in parthenogenetic eggs has now been proved: see note (#x22_pgepubid00039) at the end of this Essay; see also Essay VI (#x28_x_28_i58).—A. W., 1888.

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.

158

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

159

Hensen, ‘Centralblatt,’ 1869, No. 26.

160

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

161

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

162

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

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.

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.

165

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

166

‘Daphniden,’ Abhandlung, vi. p. 324.

167

l. c., p. 150.

168

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

169

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

170

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