A phylogenetic classification of animals (for the use of students) . Fig. 12. Primitive Hydrozoa. Three diagrammatic vertical sections (afterLankester), A, Ancestral Hydrozoon shewing a condition intermediate betweenthe Hydra-form and the Medusa-form. B, Simple Hydra-like ancestor produced bymodification of A. C, Simple Medusa-like ancestor produced by modificationof A. m, mouth; en, enteron; t, tentacle; g, reproductive organs. A, Indicatesthe same point in each form, viz., the base of the tentacle. In A it is at theequator of the globose body, in B at the top of the cylindrical body, and in
A phylogenetic classification of animals (for the use of students) . Fig. 12. Primitive Hydrozoa. Three diagrammatic vertical sections (afterLankester), A, Ancestral Hydrozoon shewing a condition intermediate betweenthe Hydra-form and the Medusa-form. B, Simple Hydra-like ancestor produced bymodification of A. C, Simple Medusa-like ancestor produced by modificationof A. m, mouth; en, enteron; t, tentacle; g, reproductive organs. A, Indicatesthe same point in each form, viz., the base of the tentacle. In A it is at theequator of the globose body, in B at the top of the cylindrical body, and in C atthe margin of the beU-shaped body. The dark inner wall of the enteron is theendoderm, the lighter outer layer of the body is the ectoderm. sexually mature detached its base, and, by enlarging itsequatorial region into a disc, and finally into a bell concaveon the oral face and provided with circularly-placed bandsof muscle, acquired a swimming organ by the contractionsof which it could be propelled through the water (seefig. 12, C). The ova and spermatozoa wer
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
