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THEORY OF CELLS.
The vegetable cell was discovered by Schleiden, Professor of Botany at Jena, in 1838. Next year Schwann found the animal cell.
In 1844 Koelliker discovered that the egg cell, by division and multiplication, becomes an aggregation—a heap of new cells.
In 1849 Huxley found the two primary layers (observed long before by Pander and Baer in the chick) also in certain Invertebrata, the Medusæ; and he called these layers 'ectoderm' and 'endoderm' respectively.
In 1851 Remak, in his 'Untersuchungen über die Entwicklung der Thiere,' showed the egg to be a simple cell, and that from it, by repeated division or multiplication, arise
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