13^ LIFE AND DEATH. [III. 



Orthonectid is an adaptation to a parasitic life, which on the 

 one side renders the possession of a stomach a superfluity, and 

 on the other demands the production of a great number of 

 germ-cells \ It is certain that the Orthonectides, as at present 

 constituted, cannot have lived in the free condition, and also 

 that their adaptation to parasitism cannot have arisen at the 

 beginning of the phyletic development of Metazoa, because they 

 inhabit star-fishes and Nemertines — both relatively highly 

 developed Metazoa. Hence it is, at any rate, doubtful whether 

 the Orthonectides can claim to pass as typical forms of the 

 lowest Heteroplastids, and whether their reproduction can be 

 looked upon ' as typical for the unknown ancestors of all Poly- 

 plastids ' (1. c, p. 45). If, however, we accept some organism 

 resembling these Orthonectides as the most ancient Hetero- 

 plastid, being a free-living organism, it must have had a 

 stomach, and the cells surrounding it must — as a whole or in 

 part — have possessed the power of digesting ; at any rate, they 

 cannot all have been germ-cells, and therefore it is improbable 

 that death would be the direct result of the extrusion of the 

 germ-cells. 



Let us now consider the manner in which Gotte has endea- 

 voured to explain the transmission of the cause of death — which 

 first appeared in the Orthonectides— from these organisms to 

 all later Metazoa, until the very highest forms are reached. 

 Exact proofs of this supposition are unfortunately wanting, and 

 the evidence is confined to the collection of a number of cases 

 in which death and reproduction take place nearly or quite 

 simultaneously. These would prove nothing, even if post hoc 

 were alw^ays propter hoc : and there are, opposed to them, a 

 number of cases in which reproduction and death take place at 



^ 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 Treraatodes, ' 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 Ortho- 

 nectides 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. Anatomic). 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). 



