PHYLOGENY OF STAR-FISHES. 169 
develops which is utterly different from the fully developed 
Star-fish, but very like the ciliated larvee of certain seg- 
mented Worms (Star-worms and Ring-worms). This peculiar 
animal-form is generally called the “larva,” but more cor- 
rectly the “nurse” of these Star-fish. It is very small and 
transparent, swims about by means of a fringe of cilia, 
and is always composed of two equal symmetrical halves 
or sides. The fully grown Echinoderm, however—which 
is frequently more than a hundred times larger, and quite 
opaque—creeps at the bottom of the sea, and is always 
composed of at least five co-ordinate pieces, or antimera, in 
_ the form of radii. Plate VIII. shows the development of the 
“nurses ” of the four Echinoderms represented on Plate IX. 
The fully developed Echinoderm arises by a very remark- 
able process of budding in the interior of the “nurse,” of 
which it retains little more than the stomach. The nurse, 
erroneously called the “larva,” of the Echinoderm, must 
accordingly be regarded as a solitary worm, which by 
internal budding produces a second generation, in the form 
of a stock of star-shaped and connected worms. The whole 
of this process is a genuine alternation of generations, or 
metagenesis, not a “ metamorphosis,” as is generally though 
erroneously stated. A similar alternation of generations 
also occurs in many other worms, especially in some star 
worms (Sipunculide), and cord worms (Nemertinz). 
Now if, bearing in mind the fundamental law of biogeny, 
we refer the ontogeny of Echinoderma to their phylogeny, 
then the whole historical development of the Star-fishes 
suddenly becomes clear and intelligible to us, whereas 
without this hypothesis it remains an insoluble mystery. 
(Compare Gen. Morph. ii. pp. 95-99.) 
