A phylogenetic classification of animals (for the use of students) . o Amoeba, further up. The large and rather heterogeneous group of organisms,known as Infusoria,* may be traced back to a point of originat the top of the Monera, and the ancestral forms wereprobably simple Monads, resembling closely the mastigopodstage in the life-history of Protomyxa, If one of the doubt-less numerous varieties of Protomyxa-like organisms, whichhave existed, had its mastigopod stage emphasised, so as tobecome the most important condition in its life, while theother stages were partly suppressed or modified,
A phylogenetic classification of animals (for the use of students) . o Amoeba, further up. The large and rather heterogeneous group of organisms,known as Infusoria,* may be traced back to a point of originat the top of the Monera, and the ancestral forms wereprobably simple Monads, resembling closely the mastigopodstage in the life-history of Protomyxa, If one of the doubt-less numerous varieties of Protomyxa-like organisms, whichhave existed, had its mastigopod stage emphasised, so as tobecome the most important condition in its life, while theother stages were partly suppressed or modified, it wouldgradually become a Monad, or simple Flagellate Infusorian(fig. 3), and such was probably the mode of origin of thisgroup of the Protozoa. Fig. 3. A Monad, one of the Flagellate Infusorians. The main line of the Infusoria leads upwards fromthese simple ancestral forms to the very much higherand more complex Ciliata; but there are several aberrantgroups, such as some of the Flagellata, the Catallacta{Magosphcera), Noctiluca, and allied forms, which must have. Fig. 4. MagosphcBra planula, Haeckel. Optical section of the colonial stage in the life-history. diverged from the axis far back, and have become evolvedin different directions. Magosphcera (fig. 4) exhibits affini- * For figures of this group, the student should consult Saville KentsMamial of the Infusoria. ties with Protomyxa, and with the Flagellata, but is morehighly differentiated; while some of the Cilioflagellata (,Peridinium) shew such striking resemblances to some of thelower plants that it is a question with some biologistswhether or not they belong to the animal series. But theresemblances are really not surprising when we consider theclose relationship between the lower Infusoria and the Proto-phyta. The common Protomyxa-like ancestor is not farremoved from either of them. In passing up to the higher Infusoria, we find thatthe Holotricha {, Paramoecium)—where besides internaldifferentiation, the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
