A phylogenetic classification of animals (for the use of students) . on, includesthe animals above the Protozoa, and may be distinguished bytwo important characteristics :—1. The body is alwaysmulticellular, being formed of more than one cell, usually ofa very large number. The few Protozoa which are composedof more than a single cell (such as some of the Infusoria—see fig. 6), are clearly colonies formed of a number of inde-pendent members, each of which is unicellular. 2. Repro-duction, though it may also be effected by budding, or someother asexual method, is always performed sexually by ov
A phylogenetic classification of animals (for the use of students) . on, includesthe animals above the Protozoa, and may be distinguished bytwo important characteristics :—1. The body is alwaysmulticellular, being formed of more than one cell, usually ofa very large number. The few Protozoa which are composedof more than a single cell (such as some of the Infusoria—see fig. 6), are clearly colonies formed of a number of inde-pendent members, each of which is unicellular. 2. Repro-duction, though it may also be effected by budding, or someother asexual method, is always performed sexually by ovaand spermatozoa; while in the Protozoa, these reproductiveelements are not found, and consequently true sexual repro-duction cannot take place. These two characters might beconsidered as one, since the second really depends upon the 12 first. As the sexual elements are equivalent to cells, they canobviously only be produced in a multicellular body. As to the method by which the unicellular Protozoabecame multicellular Metazoa, it is probable that the passage. Fig. 6. Magosphcera planula, Haeckel. Optical section of the colonial stage in the life-history. was eJBfected by some unknown colonial forms which may beplaced above Amceha, This is a more probable position forthe transition forms to occupy than the tops of any of theProtozoa groups, such as Infusoria, or Foraminifera, orRadiolaria would be, and the line stretching straightupwards from near Amoeba may be supposed to pass throughthe hypothetical compound Protozoa. In the development ofany one of the Metazoa, we see a unicellular organism
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
