BRACHIOPODA 



541 



Fig. 402. Development of Brachiopoda. A, Section of larva at end of gastrula- 

 tion showing the two coelomic pouches originating from the archenteron. 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 

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

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

 lip; M. mouth; tn.l. mantle lobe; stk. stalk; ten. tentacles; ch. chaetae; e. 

 eyes. Altered from Delage and Heronard, after various authors. 



