6l4 THE INVERTEBRATA 



into minute papillae which traverse the substance of the shell. The 

 cells, of which the papillae are composed, are often of a minutely 



di.ql. 



r 



Fig. 422. Longitudinal section of Magellania {Waldheimia) slightly to the 

 left of the middle line. After J.J. Lister, bw. body wall ; di.gl. digestive gland ; 

 h. heart; int. intestine; Ip. dorsal lip of Iph. lophophore; M. mouth; tn.d. 

 muscles running from dorsal valve to ventral ; nphr. nephrostome ; ri. vertical 

 ridge on dorsal valve; st. stomach; stk. stalk; tn. tentacles of lophophore; 

 tn.t. terminal tentacles. 



Fig. 423. Fig. 424. 



Fig. 423. Terehratula semiglobosa, Upper Chalk. A, Dorsal; B, Lateral view, 

 fl, posterior ; b, anterior ; a-b, length ; c-d, breadth ; e-f, thickness ; g-h, hinge 

 line, X f . From Woods. 



Fig. 424. Vertical section of shell of Magellania {Waldheimia) flavescens. 

 a, prismatic layer; b, periostracum ; c, outer calcareous layer; d, e, canals 

 traversing the calcareous layers, containing the mantle papillae in life. 

 After King. 



branching type which resemble the bone corpuscles of vertebrates. 

 It must be supposed that the papillae are concerned with the secretion 

 and growth of the shell. Each valve (Fig. 424) is composed of an outer 



