A phylogenetic classification of animals (for the use of students) . c, hypoblast;bl, blastopore; en, archenteron. groups of the Metazoa, his Gastrea theory, which is,that the Gastrula stage in embryology represents the Gastrea,an ancestral organism formed of two layers of cells, theouter epiblast and the inner hypoblast, enclosing a centralcavity which communicates with the exterior at one end(see fig. 8). Lankester,! on the other hand, considers thatthe Planula (fig. 9), an embryo formed like the Gastrulaof two layers of cells, but differing from it in having noopening, is more probably the
A phylogenetic classification of animals (for the use of students) . c, hypoblast;bl, blastopore; en, archenteron. groups of the Metazoa, his Gastrea theory, which is,that the Gastrula stage in embryology represents the Gastrea,an ancestral organism formed of two layers of cells, theouter epiblast and the inner hypoblast, enclosing a centralcavity which communicates with the exterior at one end(see fig. 8). Lankester,! on the other hand, considers thatthe Planula (fig. 9), an embryo formed like the Gastrulaof two layers of cells, but differing from it in having noopening, is more probably the far back common ancestorof the Metazoa. Eecently Butschli | has brought forwardarguments in favour of the Placula (fig. 10)—a simple * SUidien zur Gastrcea-theorie, Jena, 1877.+ Notes on Embryology and Classification. London, Aiinals and Magazine of Natural History^ for May, 1884. 14 flat plate or disc formed of two layers of cells, the upperepiblastic and the lower hypoblastic—being regarded as theearliest common ancestor of the Metazoa. The Placula is.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
