ANIMAL METAMORPHOSIS. 91 



push through the transparent dome of the Pluteus, which gradually 

 disappears, and the transformation is complete. The remarkable 

 point is that the young Echinus is developed out of only a portion 

 of the Pluteus, and the greater part of the latter, including the 

 skeleton, is cast away as useless. 



In the Brittle-stars the growth of development is sometimes 

 direct, the young commencing life at once in the parent form, but 

 more commonly they start from the egg as the same ciliated, jelly- 

 like substances. As they proceed to develop^ four long calcareous 

 rods are formed — two in front and two behind — with connecting 

 pieces going across in a peculiar manner, and meeting at the top 

 in a slender head (Fig. 3). On the upper part of this delicate 

 framework are placed the soft parts of the body, a clear gelatinous 

 flesh, which displays a large cavity, into which a sort of mouth 

 ever and anon admits a gulp of water. The lower parts of the 

 rods are merely encased in the flesh without any mutual connec- 

 tion. Delicate cilia cover the whole integument. Its appearance 

 is most beautiful, its colour pellucid white, except at the summit 

 and extremities of the rods, which are of a lovely rose colour. Its 

 length is about one-fortieth of an inch, and it swims in an upright 

 position, with a calm and deliberate progression. Meanwhile, a 

 small round disc is gradually produced in a particular part of the 

 body of the Pluteus ; by-and-bye, a trellis-work of lime is formed 

 over this disc, and from it five arms begin to grow out like the 

 rays of a star. A stomach, mouth, and set of water-tubes are 

 formed within the disc, the rods drop off, and a complete Brittle- 

 star is formed. Strange to say, the plane of the future star-fish is 

 not even the same as the plane of the larva, but one quite inde- 

 pendent of it and oblique to it ; and, as with the Echinus, the 

 young star does not absorb into itself the body of the larva, but 

 throws it off as so much useless lumber, flesh, rods, and all. 



The Asteroidea, or ordinary star-fishes, show the same general 

 phenomena as are characteristic of the class ; but the larvae pos- 

 sess no calcareous frame-work as do the Echini and Ophiuroidea. 

 In some the larval form possesses six or more fin-like lappets, 

 fringed with cilia, and the posterior part is prolonged into a sort 

 of pedicel, which is also covered with cilia. This was formerly 



