In the interior of this curious nurse there then develops, by a non-sexual process of generation, namely, by the formation of internal buds or germ-buds (round about the stomach), the second generation of Star-fishes, which later on become sexually ripe. This second generation, which is represented on Plate IX. in a fully developed condition, exists originally as a stock or cormus of five worms, connected at one end in the form of a star, as is most clearly seen in the sea-stars, the most ancient and original form of the star-fishes. The second generation, which grows at the expense of the first, appropriates only the stomach and a small portion of the other organs of the latter, but forms for itself a new mouth and anus. The fringe of cilia, and the other parts of the body of the nurse, afterwards disappear. The second generation (_A_ 5-_D_ 5), is at first smaller or not much larger than the nurse, whereas, by growth, it afterwards becomes more than a hundred times, or even a thousand times, as large. If the ontogeny of the typical representatives of the four classes of Star-fishes be compared, it is easily seen that the original kind of development has been best preserved in sea-stars (_A_) and sea-urchins (_C_) by inheritance, whereas in sea-lilies (_B_) and sea-cucumbers it has been suppressed according to the laws of abbreviated inheritance (vol. i. p. 212). Plate IX. shows the fully developed and sexually mature animals of the second generation from the mouth side, which, in the natural position of Star-fishes (when creeping at the bottom of the sea), in sea-stars (_A_ 6) and sea-urchins (_C_ 6), is below, in sea-lilies (_B_ 6) above, and in sea-cucumbers (_D_ 6) in front. In the centre we perceive, in all the four Star-fishes, the star-shaped, five-pointed opening of the mouth. In sea-stars, from each arm there extend several rows of little sucking feet, from the centre of the under-side of each arm to the end. In sea-lilies (_B_ 6), each arm is split and feather-like from its base upwards. In sea-urchins (_C_ 6) the five rows of sucking feet are divided by broader fields of spines. In sea-cucumbers, lastly (_D_ 6), on the worm-like body it is sometimes only the five rows of little feet, sometimes only the feathery tentacles surrounding the mouth, from five to fifteen (in this case ten), that are externally visible. PLATES X. AND XI. (_Between pages 174 and 175, Vol. II._)