PLUTEUS-METAMORPHOSIS OF ECHINUS. 



201 



of their cilia, while the marginal processes and other appendages to the 

 body remain quite passive and motionless. The first appearance of 

 metamorphosis is indicated by the development of a shield-like plate 

 (fig. 99, 2, 6), which, during the months of August and September, 



Fig. 99. 



Metamorphosis of Echinus. 1. A Pluteus with thirteen arms : A A, anterior inferior lateral 

 processes; BB, posterior inferior processes; C c, lateral processes of the vaulted disk; D, ter- 

 minal process from the apex of the vaulted disk ; E E, anterior, and F F, posterior processes of the 

 framework of the mouth ; Q G, posterior processes of the body : a, mouth ; a', basin-like under- 

 lip ; I, oesophagus ; d, stomach ; e, calcareous framework of the skeleton. 2. The same in a more 

 advanced stage of development the spines of the young Echinus beginning to make their appear- 

 ance, covered with a transparent skin : a, remnant of the calcareous skeleton of the larva or 

 Phiteus, which has now nearly disappeared ; 6, branched calcareous spicula belonging to the larva 

 skeleton ; c, spines, and d, tentacles of the young Echinus. 3. The echiniform condition almost 

 completed, only a few calcareous spicula of the larva remaining. (After Miiller.) 



becomes visible beneath the skin covering the dome of the body, sloping 

 as if inclined towards its apex, and not inaptly representing the finger- 



