He begins with the monera, the organisms of the lowest form, discovered by himself, which have not so much as the organic rank of a cell, but are only corpuscules of mucus, without kernel or external covering, called by him cytod, and arising from an organic carbon formation. The lowest and most formless moneron is the bathybius, discovered by Thomas Huxley, a network of recticular mucus, which in the greatest depths of the sea, as far down as 7,000 metres, covers stone fragments and other objects, but are also found in less depths, in the Mediterranean Sea, for instance. From the moneron he proceeds to the amoeba--a simple cell, with a kernel, which still corresponds to the egg of man in its first state. The third stage is formed by the communities of amoebae (synamoebae), corresponding to the mulberry-yolk in the first development of the fecundated egg, and to some still living heaps of amoebae. To the fourth stage he assigns the planaea, corresponding to the embryonic development of an albumen and the planula or ciliated {48} larva. When these ciliated larvae are developed, they contract themselves so as to form a cavity; and this fifth stage--especially important for his theory--he calls gastraea. In this form, he says, the progaster is already developed, and its wall is differentiated for the first time into an animal or dermal layer (ectoblast), and into a vegetative or intestinal layer (hypoblast). At the sixth stage, there branched off the prothelmis, or worms, with the first formations of a nervous system, the simplest organs of sense, the simplest organs for secretion (kidneys) and generation (sexual organs), represented to-day by the gliding worms or turbellaria; as the seventh stage, the soft worms, as he called them at first--the blood worms, or coelomati, as he describes them in his "Anthropogeny"--a purely hypothetical stage, on which a true body-cavity and blood were formed; the eighth stage are the chorda-animals with the beginning of a spinal rod, corresponding to the larva of the ascidiae. At the ninth stage, called the skull-less animals (acrania), and corresponding to the still living lancelet, we enter the series of the vertebrates. The importance of the eighth and ninth stages for the theory, we have already pointed out in our remarks upon Darwin, p. 43. The tenth stage is formed by those low fishes in which the spinal rod is differentiated into the skull--and the vertebral-column, called the single-nostriled animals (monorrhini), and represented by the cyclostoma of today (hag and lampreys). The eleventh stage is formed by the primaeval fish or selachii (sharks); the twelfth by the mud fish, of which there still live the protopterus in Africa, the lepidosiren in the tributaries of the Amazon, and the ceratodus in the swamps of Southern {49} Australia. On the thirteenth stage, there are the gilled amphibians (sozobranchia), proteus and axolotl; on the fourteenth, the tailed amphibians (sozura), newt and