70 



BRACHIOPODA. 



It is, however, not impossible, indeed, taking into account the dorsal 

 position of the lophophore-rudiment, it is probable that even before 

 the oesophageal invagination appears in the cephalic lobe of the 

 attached larva, certain displacements have taken place which alter 

 the primitive conditions (cf. Fig. 34). 



FIG. 32. Two stages in the metamorphosis of Argiope (after KOWALEVSKY). 6, provisional 

 setae ; d, rudiment of the mid-gut ; fc, cephalic lobe ; m, mantle-fold ; st, peduncle. 



The rudiment of the lophophore (Fig. 33 A,.t) arises in the form 

 of an almost circular thickening on the inner surface of the dorsal 

 mantle-lobe. As the mouth is later encircled by the lophophore, this 

 circular thickening of the cephalic lobe must extend ventrally. The 

 first tentacle-rudiments (t) are soon seen in the form of four swellings. 

 At a later stage these develop into hollow tubular outgrowths 



