[77]. Julin does not enter into further details on this point, and it is not quite clear at what precise time the cells of the ectoderm atrophy; but this is irrelevant to the origin of death, since the granular mass surrounding the egg-cells at any rate belongs to the soma of the mother.
[78]. Leuckart finds such a great resemblance between the newly born young of Distoma and the Orthonectides, that he is inclined to believe that the latter are Trematodes, ‘which in spite of sexual maturity have not developed further than the embryonic condition of the Distoma’ (‘Zur Entwicklungsgeschichte des Leberegels,’ Zool. Anzeiger, 1881, No. 99). In reference to the Dicyemidae, which resemble the Orthonectides in their manner of living and in their structure, Gegenbaur has stated his opinion that they belong to a ‘stage in the development of Platyhelminthes’ (Grundriss d. vergleich. Anatomie). Giard includes both in the ‘phylum Vermes,’ and regards them as much degenerated by parasitism; and Whitman—the latest investigator of the Dicyemids—speaks of them in a similar manner in his excellent work ‘Contributions to the Life-history and Classification of Dicyemids’ (Leipzig, 1882).
[79]. ‘Dauer des Lebens;’ translated as the first essay in this volume.
[80]. See the first essay upon ‘[The Duration of Life],’ p. [22] et seq.
[81]. ‘Ursprung des Todes,’ p. 29.
[82]. l. c., p. 5.
[83]. See the preceding essay ‘[On Heredity].’
[84]. The problem is very easily solved if we seek assistance from the principle of panmixia developed in the second essay ‘On Heredity.’ As soon as natural selection ceases to operate upon any character, structural or functional, it begins to disappear. As soon, therefore, as the immortality of somatic cells became useless they would begin to lose this attribute. The process would take place more quickly, as the histological differentiation of the somatic cells became more useful and complete, and thus became less compatible with their everlasting duration.—A. W. 1888.
[85]. See the preceding essay ‘[On Heredity.]’
[86]. See the first essay on ‘[The Duration of Life].’