ECHINODERM-LARV.E 



-BIPINNARIA. 



5(59 



Star-fish and Sand-stars have usually neither Intestinal tube nor 

 Anal orifice, their Larval Zooids, like those of other Echinoderms, 

 always possess both. The external forms of these Larvae, how- 

 ever, vary in a most remarkable degree, owing to the unequal 

 evolution of their different parts ; and there is also a considerable 

 diversity in the several Orders, as to the proportion of the fabric 

 of the Larva which enters into the composition of the Adult form. 

 In the fully-developed Star-fish and Sea-urchin, the only part 

 retained is a portion of the stomach and intestine, which is 

 pinched-off, so to speak, from that of the Larval Zooid. 



441. One of the most remarkable forms of Echinoderm Larva? 

 is that which has received the name of Bipinnaria (Fig. 296), 

 from the symmetri- 

 cal arrangement of p IG 296. 

 its natatory organs. 

 The Mouth (a), which 

 opens in the middle 

 of a transverse fur- 

 row, leads through 

 an Oesophagus a' to 

 a large Stomach, 

 around which the 

 body of a Star-fish 

 is developing itself ; 

 and on one side of 

 this mouth is ob- 

 served the Intestinal 

 tube and Anus (b). 

 On either side of the 

 anterior portion of 

 the body are six or 

 more narrow Fin-like 

 appendages, which 

 are fringed with 

 Cilia; and the pos- 

 terior part of the 

 body is prolonged 

 into a sort of 

 pedicle, bilobed to- 

 wards its extremity, 

 which also is covered 

 with Cilia. The or- 

 ganization of this 

 Larva seems com- 

 pleted, and its move- 

 ments through the water become very active, before the mass at 

 its anterior extremity presents anything of the aspect of the Star- 

 fish; in this respect corresponding with the movements of the 



Bipinnaria asterigera, or Larva of Star-fish : 

 —a, Mouth ; 'a', (Esophagus ; b, Intestinal tube 

 and Anal orifice ; c, furrow in which the mouth 

 is situated ; d d', bilobed peduncle ; 1, 2, 3, 4, 5, 

 6, 7, Ciliated Arms. 



