[87]. See the first essay on ‘[The Duration of Life].’
[88]. These assumptions can be authenticated among the Infusoria. The encysted Colpoda cucullus, Ehrbg. divides into two, four, eight, or sixteen parts; Otostoma Carteri, into two, four, or eight; Tillina magna, Gruber, into four or five; Lagynus sp. Gruber, into two; Amphileptus meleagris, Ehrbg. into two or four. The last two species and many others frequently do not divide at all during the encysted condition. But while any further increase in the number of divisions within the cyst does not occur in free-swimming Infusoria, the interesting case of Ichthyophthirius multifiliis, Fouquet, shows that parasitic habits call forth a remarkable increase in the number of divisions. This animal divides into at least a thousand daughter individuals.
[89]. True development also takes place in the above-mentioned Ichthyophthirius. While in other Infusoria the products of fission exactly resemble the parent, in Ichthyophthirius they have a different form; the sucking mouth is wanting while provisional clasping cilia are at first present. In this case therefore the word germ may be rightly applied, and Ichthyophthirius affords an interesting example of the phyletic origin of germs among the lower Flagellata and Gregarines. Cf. Fouquet, ‘Arch. Zool. Expérimentale,’ Tom. V. p. 159. 1876.
[90]. Bütschli, long ago, doubted the application of the fundamental law of biogenesis to the Protozoa (cf. ‘Ueber die Entstehung der Schwärmsprösslings der Podophrya quadripartita,’ Jen. Zeit. f. Med. u. Naturw. Bd. X. p. 19, Note). Gruber has more recently expressed similar views, and in fact denies the presence of development in the Protozoa, and only recognizes growth (‘Dimorpha mutans, Z. f. W. Z.’ Bd. XXXVII. p. 445). This proposition must however be restricted, inasmuch as a development certainly occurs, although one which is coenogenetic and not palingenetic.
[91]. See the first essay on ‘The Duration of Life,’ p. [23] et seq.
[92]. See Appendix to the first essay on ‘The Duration of Life,’ pp. [43]-46.
[93]. See the first essay on ‘The Duration of Life,’ p. [21].
THE CONTINUITY OF THE GERM-PLASM