| Fig I. | Fig. II. | Fig. III. |
Fig. I.—Appendicularia, seen from the left side, m, mouth; k, gill intestine; o, œsophagus; v, stomach; a, anus; n, nerve ganglia (upper throat-knots); g, ear vesicle; f, ciliated groove under the gill; h, heart; e, ovary; c, notochord; s, tail.—Haeckel.
Fig. II.—Represents Sack Worms (Himatega), and is the structure of an Ascidian, seen from the left. sb, gill-sac; v, stomach; i, large intestine; c, heart; t, testes; vd, seed duct; o, ovary; o', matured eggs in the body cavity. After Milne-Edwards.
Fig. III.—Represents the Acrania Series. Lancelet (Amhioxus Lanceolatus), twice the actual size, seen from the left. a, mouth-opening, surrounded by cilia; b, anal-opening; c, ventral-opening (Porus abdominalis); d, gill-body; e, stomach; f, liver-cœcum; g, large intestine; h, cœlum; i, notochord (under it the aorta); k, arches of the aorta; l, main gill-artery; m, swellings on its branches; n, hollow vein; o, intestinal vein.—Haeckel.]
Fig. I.
Fig. I.—Represents the Monorhina Series. Lamprey (Petromyzon Americanus) from the Atlantic—Orton.