Essays Upon Heredity and Kindred Biological Problems

121

According to the observations of Nussbaum and van Beneden, the egg of Ascaris departs from the ordinary type, but I think that the latter observer goes too far when he concludes from the form of the nuclear spindle (of which the two halves are inclined to each other at an angle) that we have before us a process entirely different from that of ordinary nuclear division.

122

Trinchese, ‘I primi momenti dell’ evoluzione nei molluschi,’ Atti Acad. Lyncei (3) vii. 1879, Roma.

123

M. Nussbaum, ‘Archiv für Mikroskopische Anatomie,’ Bd. XVIII und XXIII.

124

Valaoritis, ‘Die Genesis des Thier-Eies.’ Leipzig, 1882.

125

Kölliker, ‘Die Bedeutung der Zellkerne,’ etc.; Zeitschr. f. wiss. Zool. Bd. XLII.

126

‘Compt. rend.’ Tom. LIV. p. 150.

127

‘Entwicklung der Dipteren.’ Leipzig, 1864.

128

‘Zeitschr. f. wiss. Zool.’ Bd. XVI. p. 389 (1866).

129

‘Compt. rend.’ Nov. 13, 1882.

130

Grobben, ‘Arbeiten d. Wien. Zool. Instituts,’ Bd. II. p. 203.

131

Bütschli, ‘Zeitschrift f. wiss. Zool.’ Bd. XXIII. p. 409.

132

‘Science,’ vol. iv. No. 90, 1884.

133

Among unicellular organisms, encysted individuals are often called germs. They sometimes differ from the adult organism in their smaller size and simpler structure (Gregarinidae), but they represent the same morphological stage of individuality.

134

Compare Bütschli in Bronn’s ‘Klassen und Ordnungen des Thierreichs,’ Bd. I. p. 777.

135

Gustav Jäger, ‘Lehrbuch der Allgemeinen Zoologie,’ Leipzig, 1878; II. Abtheilung. Probably on account of the extravagant and superficial speculations of the author, the valuable ideas contained in his book have been generally overlooked. It is only lately that I have become aware of Jäger’s above-mentioned hypothesis. M. Nussbaum seems to have also arrived at the same conclusion quite independently of Jäger. The latter has not attempted to work out his hypothesis with any degree of completeness. The above-mentioned observations are followed immediately by quite valueless considerations, as, for instance, that the ontogenetic and phyletic groups are in concentric ratio! The author might as well speak of a quadrangular or triangular ratio!

136

[Facts of the same kind are also known in the Vascular Cryptogams, Muscineae, Characeae, Florideae, etc.—S. S.]

137

Weismann, ‘Die Entstehung der Sexualzellen bei den Hydromedusen.’ Jena, 1883.

138

[I adopt this term, suggested by E. Ray Lankester and G. C. Bourne, as the name of the supporting lamina of Coelenterata. See ‘Quart. Journ. Microsc. Sci.’ Jan. 1887, p. 28.—E. B. P.]

139

Dr. Clemens Hartlaub, ‘Ueber die Entstehung der Sexualzellen bei Obelia.’ Freiburg, Inaugural Dissertation: see also ‘Zeitschrift für wissenschaftliche Zoologie.’ Bd. XLI. 1884.

140

English translation, by H. Marshall Ward. Oxford, 1887, Clarendon Press.

141

[Such gland-cells are known in both animals and plants. See W. Gardiner and Tokutaro Ito, On the structure of the mucilage-secreting cells of Blechnum occidentale L., and Osmunda regalis L., ‘Annals of Botany,’ vol. i. p. 49.—S. S.]

142

Thus in 1877 Bütschli thought that ‘the chief significance of the formation of polar bodies lies in the removal of part of the nucleus of the egg, whether this removal is effected by simple expulsion or by the budding of the egg-cell.’ ‘Entwicklungsgeschichtliche Beiträge;’ Zeitschrift für wissenschaftliche Zoologie, Bd. XXIX. p. 237, footnote.

143

C. S. Minot, ‘Account, etc.;’ Proc. Boston Soc. Nat. Hist. vol. xix. p. 165, 1877.

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.

145

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