31 



structure and function as the slieath in other forms .tliough 

 no style is formed. As the intestine has loft its median 

 position at the extreme posterior end of the stomach in 

 the development of more specialized forms, it has reraained 

 attached to various parts of the sheath of the style, as 

 in Oardium, and has reached its greatest displacement in 

 forms like Teredo and Pholas, in v/hich it leaves the stom- 

 ach from one side, and in which the sheath of the style 

 forms a large blind pouch. If this view of the relations 

 of the stomach, intestine, and sheath be the correct one, 

 then the slieath is not a structure which has been acquired 

 in the more highly specialized forms. It is homologous 

 with the posterior part of the stomach of primitive forms 

 like !Tucula and Yoldia, while the intestine has left its 

 original madian attacliment to the posterior end, to be at- 

 tached to one side of, the stomach. 



b. The General Organization of the Adult. 



After the preceding description of the Ip.rva and its 

 metamorphosis, the general plan of the adult ".,i.ip-v/orm" 



