70 



BRACHIOPODA. 



It is, hoAvever, 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 Avhich alter 

 the primitive conditions {cf. Fig. 34). 



wi 





^i| '^ whir'' 



m III! / 



Fig. 32. — Two stages in the iiietainorphosis of Argiopc (after Kowalevsky). b, provisional 

 setae ; d, rudiment of the mid-gut ; k, 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 



