92 ANIMAL METAMORPHOSIS. 



described as a distinct organism under the name of Bipinnaria 

 (Fig. 2). 



The common five-fingered star-fish, immediately after exclusion 

 from the egg, presents an ovoid, sub-spherical shape. It remains 

 for some time attached to the sides of the incubatory cavity of the 

 parent. After a few days, four club-shaped appendages begin to 

 appear, sprouting, as it were, from the anterior extremity of the 

 body. It swims about vivaciously, with the four arms in advance, 

 by means of vibratile cilia. By degrees, the body assumes a pen- 

 tagonal outline, from the angles of which five blunt rays begin to 

 grow. It now ceases to swim, and sinks to the bottom of the sea, 

 where it goes on increasing in size for two or three years, the 

 blunt knobs gradually lengthening out into pointed rays, and the 

 animal takes on the form of the ordinary star-fish, with which we 

 are all familiar. 



When first seen, no one could suspect that the Pentacrinus 

 Europeus was the young stage of a star- fish, the Comatula or 

 feather-star. In its first stage, the larval Comatula presents itself 

 as a cylindrical, jelly-like body, furnished with an alimentary 

 canal having a lateral aperture, and four transverse bands of cilia. 

 It swims about freely in this condition for some time, when lime- 

 plates begin to form, in the shape of a cup, in the upper part of 

 its body; while below these, other and smaller plates take the form 

 of a stalk (Fig. 4). After a time, the whole sinks to the bottom 

 of the sea, and attaches itself, by a strong lime-plate, to some 

 marine object, where it remains, looking like a stony plant (Fig. 5). 

 From the cup are developed ten radiating arms, produced by the 

 splitting into two of live primary rays, and it is thus transformed 

 into a Pentacrinus^ or stone-lily. When sufificiently matured, the 

 body drops off the stalk, and again assumes a free condition of 

 existence as a fully developed Comatula (Fig. 6). 



The last order of the Echinodermata comprises the Holothu- 

 rians, or sea-cucumbers. The young Holothurian, on leaving the 

 egg, develops into a barrel-shaped, transparent larva (Fig. 7), 

 without any skeleton, but surrounded by transverse rows of cilia, 

 by means of which it swims about, rapidly rotating on its long 

 axis. In this stage it used to be described as a distinct genus, 

 under the name of Auricularia, As it advances in growth, it 



