Was Man Created?

by Henry A. Mott

Fig I.	Fig. II.	Fig. III.

Figs. I and II.—Represents the next higher stage (Tubularia). Fig. I, a simple Gliding Worm (Rhabdocœlum); m, mouth; sd, throat-epithelium; sm, throat-muscles; d, stomach-intestine; nc, kidney-ducts; nm, opening of the kidneys; au, eye; na, nose-pit. Fig. II, the same Gliding Worm, showing the remaining organs; g, brain; au, eye; na, nose-pit; n, nerves; h, testes; ♂, male opening; ♀, female opening; e, ovary; f, ciliated outer-skin.—Haeckel.

Fig. III.—Represents Soft Worms (Scolecida) and is a young Acorn Worm (Balanoglossus), after Agassiz. r, acorn-like proboscis; h, collar; k, gill-openings and gill-arches of the anterior intestine, in a long row, one behind the other, on each side; d, digestive posterior intestine, filling the greater part of the body cavity; v, intestinal vessel, lying between two parallel folds of the skin; a, anus.

Out of the planula, then, develops an exceedingly important animal form—the gastrula (that is, larva with a stomach or intestine), which resembles the planula, but differs essentially in the fact that it encloses a cavity which opens to the outside by a mouth. The wall of the progaster (primary stomach) consists of two layers of cells: an outer layer of smaller ciliated cells (outer skin or ectoderm), and of an inner layer of large non-ciliated cells (inner skin or entoderm). This exceedingly important larval form, the "gastrula," makes its appearance in the ontogenesis of all tribes of animals. These gastræada must have existed during the older primordial period, and they must have also included the ancestors of man. A certain proof of this is furnished by the amphioxus, which, in spite of its blood relationship to man, still passes through the stage of the gastrula with a simple intestine and a double intestinal wall.[16] By motion of the cilia or fringes of the skin-layer, the gastræa swam freely about in the Laurentian ocean.

The development of the gastræa now deviated in two directions—one branch of gastræads gave up free locomotion, adhered to the bottom of the sea, and thus, by adopting an adhesive mode of life, gave rise to the proascus, the common primary form of the animal plants (zoophyta). The other branch was originated by the formation of a middle germ-layer or muscular layer, and also by the further differentiation of the internal parts into various organs; more especially, the first formation of a nervous system, the simplest organs of sense, the simplest organs for secretion (kidneys), and generation (sexual organs)—this branch is the prothelmis, the common primary worms (vermes). Like the turbellaria of the present day, the whole surface of their body was covered with cilia, and they possessed a simple body of an oval shape, entirely without appendages. These acœlomatous worms did not as yet possess a true body cavity (cœlom) nor blood. No member of the next higher animals are in existence, neither are there any fossil remains, owing to the soft nature of their body. They are therefore called soft worms, or scoleceda. They developed out of the turbellaria of the sixth stage by forming a true body cavity (a cœlom) and blood in their interior. The nearest still living cœlomati is probably the acorn worms (balanoglossus). The form value of this stage must, moreover, have been represented by several different intermediate stages.

Out of the four different groups of the worm tribe, the four higher tribes of the animal kingdom were developed—the star-fishes (echinoderma) and insects (arthropoda) on the one hand, and the molluscs (mollusca) and vertebrated animals (vertebrata) on the other. Out of certain cœlomati, the most ancient skull-less vertebrata were directly developed. Among the cœlomati of the present day, the ascidians are the nearest relatives of this exceedingly remarkable worm, which connect the widely differing classes of invertebrate and vertebrate animals. To these animals have been given the name of sack-worms (himatega). They originated out of the worms of the seventh stage by the formation of a dorsal nerve marrow (medulla tube), and by the formation of the spinal rod (chorda dorsalis) which lies below it. It is just the position of this central spinal rod or axial skeleton, between the dorsal marrow on the dorsal side and the intestinal canal on the ventral side, which is most characteristic of all vertebrate animals, including man, but also of the larvæ of the ascidia.

We now come to the second half of the series of human ancestors. The skull-less animal lancelet, which is still living, affords a faint idea of the members of this group (acrania). Since this little animal, in its earliest embryonic state, entirely agrees with the ascidia, and in its further development shows itself to be a true vertebrate animal, it forms a direct transition from the vertebrata to the invertebrata.