274 HAECKEL 



more correctly, an oval body consisting of two 

 layers of cells and having a hole at one pole — in 

 other words, a creature with nothing but skin, 

 stomach, and mouth — was found, curiously enough, 

 in other animals besides the medusae, corals, and 

 sponges. We have the same course of develop- 

 ment in representatives of the most varied groups 

 of animals. There are worms, star-fishes, crabs, 

 and snails that develop in the same way. In fact, 

 it was proved in this very year (1867) that the lowest 

 of the vertebrates, the amphioxus (or lancelet), 

 develops in the same way. And this was not all. 

 In the ontogeny of all the higher animals right 

 up to man (inclusive) we find a state of things 

 that most closely resembles the same development. 

 At all events, the fertilised ovum gives rise in all 

 cases to a cluster of cells ; this cluster forms 

 something like a flattened or elongated vesicle 

 with a single-layered wall ; the single layer of cells 

 is doubled, and in the building up of the body one 

 half makes the external coat or skin and the other 

 half the internal lining or membrane. Haeckel 

 reflected on the whole of the facts, and drew 

 his conclusions. This very curious agreement 

 in the earlier embryonic forms must be interpreted 

 in terms of the biogenetic law. In the case of 

 the higher animals the forms have been profoundly 

 modified by cenogenesis. In the lower animals 

 they are almost or altogether a pure recapitulation 

 of the real primitive course of the development 

 of the animal kingdom. In the earliest times 

 animals were evolved in something like the follow- 



