558 B1PINNARIA. 



known as brachiolar arms, and the larvae provided with them 

 as Brachiolaria (fig. 259 D). 



As a rule the following arms can be distinguished (fig. 259 C and D), on 

 the hinder ring (Agassiz' nomenclature) a median anal pair, a dorsal anal 

 pair, and a ventral anal pair, a dorsal oral pair, and an unpaired anterior 

 dorsal arm ; on the pras-oral ring a ventral oral pair, and sometimes (Miiller) 

 an unpaired anterior ventral arm. 



The three brachiolar arms arise as processes from the base of the 

 unpaired dorsal arm, and the two ventral oral arms. The extent of the 

 development of the arms varies with the species. 



FIG. 259. DIAGRAMMATIC REPRESENTATION OF VARIOUS FORMS OF ASTEROID 

 LARVAE. A, B, C, BIPINNARIA; D, BRACHIOLARIA. (Copied from Miiller.) 

 The black lines represent the ciliated bands; and the shading the space between 

 the pne-oral and the post-oral bands. 



HI. mouth ; an. anus. 



The changes by which the Bipinnaria or Brachiolaria becomes 

 converted into the adult starfish are very much more complicated 

 than those which take place in Holothurians. For an accurate 

 knowledge of them we are largely indebted to Alex. Agassiz 

 (No. 543). The development of the starfish takes place entirely 

 at the posterior end of the larva close to the stomach. 



On the right and dorsal side of the stomach, and externally 

 to the rigJit peritoneal space, are formed five radially situated 

 calcareous rods arranged in the form of a somewhat irregular 

 pentagon. The surface on which they are deposited has a 

 spiral form, and constitutes together with its calcareous rods, the 



