ABSTRACT
The mode of generation of the reproductive elements and their relation to the cells of the parental tissues, is a problem which has always made heavy demands on the labours of microscopical investigators, whether zoological or botanical ; and although an immense literature has grown about the subject since Flourens thought embryos were formed “tout d’un coup,” at the moment of the fusion of the sexual elements, it may be safely asserted that not until the last few years has any very definite knowledge been acquired, and only in a limited number of cases has it yet reached any high degree of accuracy.
“Vergleich der Ei und Samenbildung bei Nematoden. Eine Grundlage für cellulare Streitfragen,” ‘Archiv f. mikroskop. Anat.,’ Bd. xxxvi, 1890.
‘Studies of Reproductive Elements.’
‘Archiv mikro. Anat.,’ Bd. xl, p. 102.
‘Archiv für mikros. Anat.,’ Bd. xxxiv, Tafel 3.
“Ueber die Befruchtung des Axolotleies,” ‘Anatomiseher Anzeiger,’ vii, pp. 818—821.
The results of a re-examination of the facts of Mammalian spermatogenesis have shown that the centrosomes are incorporated in the spermatozoa in the position of the Mittelstück of Amphibia, while a portion of the archoplasm is applied to the pointed extremity of the head. Field has shown that the archoplasm “Nebenkern “of Echinoderms is incorporated together with the centrosomes as the Mittelstück.
Herbert Spencer suggests that cell division becomes a necessity in virtue of the continual decrease of the absorptive area proportionally to the growth of the cell.
“Nouvelles recherches sur la fécondation et la division mitosique chez l’ascaride mégalocéphale,” ‘Bullet, de l’Académie Royal de Belge,’ 3me sér., c. xix, 1887. “Befruchtung und Theilung des thierischen Eies,” ‘Morph. Jahrb.,’ 1875.
‘Arch. f. mikros. Anat.,’ Bd. xxxvii.
Compare vom Rath and Ishikawa, loc. cit.
Compare vom Rath’s figs., loc. cit.
When sufficiently high powers are used the appearance is almost identical with the coarse vacuolation in the ectosarc of Amoeba and other protozoa.
‘Arch, fiir mikroskop. Anat.,’ Bd. xxxvii, pp. 569—582.
I do not mean to maintain that there are no other controlling factors in the formation of a definite number of chromosomes ; this cannot be the case on account of the wide difference in the size of the nuclei of tissues of the same animal. At the same time we have no knowledge of the reticulum as related to different cellular dimensions.
In connection with this see Valentine Hacker, “Die heterotjpische Kerntheilung im Cyklus der generation Zellen,” * Berichteder Naturforschenden Gesellschaft zu Freiburg,’ Bd. vi, 1892, pp. 160—188.
Professor Farmer has kindly shown me some preparations of Lilium which give exactly the same bundles of fibres related to separate granules, any one of which might be individually considered as a centrosome.
For an account of this see the description of Siebold’s results in the ‘Klassen und Ordnungen des Thier Reichs,’ pp. 960—962. Also H. M. Barnard’s ‘Apodidæ.’
‘Arch, für micro. Anat.,’ Bd. xxxix.
