86 SURVEY OF THE REPEODUCTIVE PROCESS 



which are prolonged into straight slender legs, strengthened 

 by filiform rods of calcareous matter reaching to the summit 

 of the dome. The mouth projects as a proboscis from the 

 middle of the concave base, and the circle of cilia surround- 

 ing it fringes the circumference of the base of the pyramid, 

 and the four projecting processes, which in swimming are 

 directed forwards. 



The new process of organization always originates in a 

 diverticulum of the dorsal integument of the germ, which 

 grows inward and lays the foundation of the future water- 

 vascular system, on which the other organs of the Echino- 

 derm are subsequently modelled. 



In Holothuria, the new formation amalgamates to a great 

 extent with the germ structures, and no part is absolutely 

 cast off, though the original mouth is obliterated, and a 

 new one formed on what was the dorsal aspect of the Auri- 

 cularia. In the Echinidae and Ophiuridse, and also in the 

 Asteridse, a new mouth is formed much in the same way ; 

 but the only organ of the original appropriated by the 

 Echinoderm is the alimentary canal. As development ad- 

 vances, a difference appears in the two cases, for while the 

 unappropriated part of the Pluteus vanishes, the Bipinnaria 

 retains its original form more persistently, and gTadually 

 becomes detached from the Starfish. The latter then sinks 

 to the bottom, and creeps by its newly developed sucking 

 feet, while the protomorphic zooid — eviscerated as it is by 

 the process — still swims about for some time as before, but 

 eventually perishes.* 



No alternation of forms is known to occur in this class, 

 after the acquisition of the typical organization, nor any 

 phenomena at all of the nature of gemmation, except we 

 are to consider the development of the sexual organs, or 

 the regeneration of lost parts, as rudimentary manifestations 



* An. Nat. Hist., 2d Ser., Till., p. 4. 



