APPENDIX. 389 



which, keep the microscopically small and transparent nnrse 

 swimming about freely in the sea. This fringe of cilia is marked 

 in Fig A 2 — A 4, on Plate VII., by the narrow alternately light 

 and dark seam. The nurse then, in the first place, forms a per- 

 fectlysimple intestinal canal for nutrition, mouth (0), stomach (m), 

 and anus (a). Later, the windings of the fringe of cilia become 

 more complicated, and there arise arm-like processes (Fig. A 3 — 

 D 3). In sea-stars (J. 4) and sea-urchins ( C 4 ) these arm- 

 like processes, which are fringed with cilia, afterwards become 

 very long. But in the case of sea-lilies (B 3) and sea-cucumbers 

 (J) 4), instead of this, the fringe of cUia, which at first, through 

 winding in and out, forms one closed ring, changes subsequently 

 into a succession of separate ciliated girdles, one lying behind 

 the other. 



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 origiual 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 dis- 

 appear. The second generation (J. 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 (G) by inheritance, whereas in 

 sea-lilies (B) and sea-cucumbers it has been suppressed accord- 

 ing to the laws of abbreviated inheritance (vol. i. p. 212). 



