[251]. In the summer-eggs of Rotifera I have, together with Mr. Ischikawa, observed one polar body, and we were able to establish for certain that a second is not formed. The nuclear spindle had already been observed by Tessin, and Billet had noticed polar bodies in Philodina, but without attaching any importance to their number. These latter observations were not conclusive proofs of the formation of polar bodies in parthenogenetic eggs, so long as it was not known whether the summer-eggs of Rotifera may develope parthenogenetically, or whether they can only develope in this way. Knowing now that parthenogenetic eggs expel only one polar body, we may perhaps be permitted to draw the conclusion that the summer-egg of a Rotifer (Lacinularia) which expelled only one polar body must have been a parthenogenetic egg. But I may add that we have also succeeded in directly proving the occurrence of parthenogenesis in Rotifera, as will be described in detail in another paper.
[252]. See Essay IV, Part III. p. [225].
[253]. E. Bessels, ‘Die Landois’sche Theorie, widerlegt durch das Experiment.’ Zeitschr. f. wiss. Zool. Bd. XVIII. p. 124. 1868.
[254]. l. c., p. 110.
[255]. Strasburger, ‘Neue Untersuchungen über den Befruchtungsvorgang bei den Phanerogamen als Grundlage einer Theorie der Zeugung.’ Jena, 1884.
[256]. Wilhelm Roux, ‘Ueber die Bedeutung der Kerntheilungsfiguren.’ Leipzig, 1884.
[257]. E. van Beneden, ‘Recherches sur la maturation de l’œuf, la fécondation et la division cellulaire.’ Gand et Leipzig, Paris, 1883.
[258]. J. B. Carnoy, ‘La Cytodiérèse de l’œuf, la vésicule germinative et les globules polaires de l’Ascaris megalocephala.’ Louvain, Gand, Lierre, 1886.
[260]. Wilhelm Roux, ‘Beiträge zur Entwicklungsmechanik des Embryo,’ No. 3, Breslauer ärztliche Zeitschrift, 1885, p. 45.