BRACHIOPODA 



617 



arch^ 



arm /(|^ ^ P'.^- 'V^^^ 



mM^^. 



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Fig. 427. Development of Brachiopoda. A, Section of larva at end of 

 gastrulation showing the two coelomic pouches originating from the archen- 

 teron. B, Larva divided into three regions. C, Differentiation of the preoral 

 region (oblique shading) and mantle lobes (stippling). D, Turning forward 

 of mantle lobes and shrinking of preoral region. E, Appearance of the arms 

 of the lophophore (one shown), preoral region now represented by lip. F, In- 

 ternal view of dorsal valve showing the first stage in development of lopho- 

 phore as a tentacular ring. G, Further development by extension of the dorsal 

 lip and the division of the ring into two arms. The ciliated groove is indicated 

 by stippling and the movement of food to the mouth by arrows. H, Larva 

 oi Lingula, corresponding to F. al.c. alimentary canal; An. anus; arch, arch- 

 enteron ; arm, one arm of the lophophore ; coe. coelomic pouch ; Ip. dorsal lip ; 

 M. mouth; w./. mantle lobe; stk. stalk; ten. tentacles; ch. chaetae; e. eyes. 

 Altered from Delage and Herouard, after various authors. 



