appears with the metamorphosis into the adult form. 



The larval organ is also homologous with the 

 stall: of Antedon although in the pphiurid larva it 

 never functions as an attachment organ. When swimming 

 the larval organ precedes. It is filled with a net- 

 work of mesenchyme cells. 



Internally the changes have- been even greater 

 than the external ones we have- just considered for 

 it is during this period of development that the 

 rotation and readjustment of organs takes place which 

 ic present in all echinoderms at come stage of their 

 development. 



The hydrocoele, which had begun its rotation 

 about the oesophagus as an axis in "C" , has complet- 

 ed it in "D" and reached its definitive position. 

 That part of the hydrocoele which ,in "C" ,was sit- 

 uated on the left of the plane dividing the larva 

 into bilaterally symmetrical halves now lies on the 

 right side of the same plane, and vice- versa. Compare 

 Figs.G and 9. 



A revolution of 100 degrees has taken place 

 in the hydrocoele since "C" to which if the 100 de- 

 grees of rotation be added which too': place up to 

 the time of "C" we have a total rotation of 360 de- 



