In revising the species of the Diplodinium (sub-genus Polyplastron) the author comes to the conclusion that on the basis of the generic criteria in the family Ophryoscolecidae, two distinct genera cannot be erected as was done by Kofoid and MacLennan (the genera Polyplastron and Elytro -plastron). On the contrary it is justifiable to include both of these species in Polyplastron (Dogiel, 1927) as a subgenus of the genus Diplodinium. In conformity with the international rules of zoological nomenclature, the correct names of both species in question are as follows: D. (Polyplastron) multivesiculatum Dogiel and Fedorowa, 1925, D. (Polyplastron) hegneri Becker and Talbott, 1927. Evidence is put forward to show how incorrect is the erection of Dogiel's aberrations P. multivesiculatum ‘confluens’ (monoscutum) and P. multivesiculatum ‘fenestratum’ into separate species, and how these forms are to be considered only as individual varieties. These views are supported by the author's own investigations on live and fixed (stained) material.
The author agrees with Kofoid and MacLennan that Polyplastron had evolved from forms related to D. (Eudiplodinium) affine, and brings forward arguments resulting from his investigations as to how this relation can be clearly disclosed. He also gives a scheme of the systematic position and phylogenetical relationship of the species in question of Diplodinium--sub-genus Polyplastron.
Conclusions are drawn concerning the relation and kinship of P. multivesiculatum and P. hegneri, as well as the author's rules in regard to the development of new contractile vacuoles, also the reasons for the development of the skeleton and the position and form of skeletal plates. These skeletal plates serve for a general strengthening of the body besides other functions.
It is argued that adaptation is a motive factor in the evolution (the selection appears as an ‘incidental selection’), while the oecologic factors and the factors of the mechanical and geographical isolation of the ruminant-hosts (in harmony with the peros manner of infection of the ruminants by these Infusoria) act as regulative factors. These two categories of factors are in diverse dimensions (they are non-equivalent and inadequate). The evolution of characters cannot be considered singly, but only species as units, and this evolution is not a result of isolated factors but of a series of factors permanently acting in reciprocal dependence. The author considers this method of analysis applicable also to other systematic groups.
- Copyright © 1935 by the Company of Biologists Ltd.