METAMORPHOSIS. 7 



ciliated ring. The lost larval organs in the oral region consequently 

 have to be replaced by extensive regeneration. It has already been 

 mentioned that the rudiment of the permanent crown of tentacles 

 which soon assumes the form of a horseshoe -shaped lophophore 

 appears early. 



FIG. 4. A series of stages in the metamorphosis of Phoronis from the Actinotrocha (after 

 METSCHNIKOFF, from BALFOUR'S Text-book). A, young larva. B, larva after the develop- 

 ment of the post-oral ring of tentacles. C, larva in which the invagination (iv) is com- 

 mencing, from which is derived the greater part of the body of the Phoronis. D, 

 invagination partially, and E, completely everted, an, anus ; m, mouth. 



By means of this remarkable metamorphosis, an animal is pro- 

 duced the body of which is derived for the greater part from a 

 prolongation of the ventral side of the larva. The dorsal side, on 

 the contrary, has undergone considerable abbreviation, and can be 

 recognised in the short tract lying between the mouth and the anus. 



