238 



the "pupa" or second form of the Auricularia is very large and 

 the tentacles do not project beyond the body, as they afterwards 



ing Holothurian. In a succeeding stage the tentacles begin to 



the oesophagus, stomach, intestine and anus are developed, and 



The madreporjc body (6) has not yet been drawn within the body. 



Fig. 109. 



Finally, the Auricularia becomes wholly absorbed, the tentacles 

 are much branched and capable of retraction within the body ; the 

 tegument secretes limestone plates, the suckers are developed in 

 the ambulacral rows and the adult form is attained without import- 

 ant changes. Fig. 83 represents a common sea-cucumber of our 



Some holothurians, as well as starfishes and ophiurans, as ob- 

 served by Mr. A. Agassiz, undergo their larval (i. e., Plnteus, 

 Brachiolaria and Auricularia) phases of development above 

 described without leaving the parent, in pouches held over the 

 mouth of the parent, making their escape in a form approaching 

 that of the adult. 



