80 



BRACHIOPODA. 



of the Brachiopoda and that of the Phylactolaematous Bryozoa have 

 been pointed out by BLOCHMANN (No. 4). The chief of these is 

 that, in consequence of the extension of the epistomal cavity (larger 

 brachial sinus) in the Brachiopoda, the lophophoral cavity is so 

 circumscribed as to be reduced to a canal running below the row 

 of tentacles (smaller brachial sinus) ; this canal then appears to be 

 cut through twice in transverse sections (a, a') through the lopho- 



A 



FIG. 41. Diagram illustrating the structure of a Brachiopod (after preparations of Terebratdla 

 corianica; cf. Figs. 5, p. 9, and 28, p. 57). A, lateral view of the lophophore. Most of the 

 tentacles are supposed to have been cutaway. B, median section. The spiral arms are cut 

 somewhat laterally to show the large brachial sinus, a, smaller brachial sinus ; a', the same 

 in dorsal transverse section ; b, larger brachial sinus (epistomal cavity) ; ds, dorsal shell- 

 valve ; ed, hind-gut ; ep, epistome (brachial fold) ; ep', the same in dorsal transverse section ; 

 Ji, heart ; m, mouth ; mg, stomach ; ms, mesentery ; mt, mantle-fold ; n, nephridium ; 

 oe, oesophagus ; s, lateral arm ; sg, supra-oesophageal ganglion ; sp, spiral arm ; st, peduncle ; 

 t, ventral tentacle ; t 1 , dorsal tentacle ; vg, ventral ganglion ; vs, ventral shell-valve. 



phore-arms, as also does the epistomal fold (brachial fold ep, ep'). 

 These differences are, indeed, very easily explained through the 

 higher differentiation which has arisen from the simpler type 

 retained in the Phylactolaemata. 



From the condition of the lophophore arid the position of the 

 epistome it follows that the shell-valve, known as the dorsal valve, 

 corresponds in position to the anal side of the body in the Bryozoa, 



