[ 283] 



On Ciliary Mechanisms in Brachiopods and some Poly- 

 chsetes, with a Comparison of the Ciliary Mechanisms 

 on the Gills of Molluscs, Protochordata, Brachiopods, 

 and Cryptocephalous Polychsetes, and an Account of 

 the Endostyle of Crepidula and its Allies. 



By 

 J. H. Orton, B.Sc, A.R.C.Sc. 



With twelve Figures in the Text. 



TABLE OF CONTENTS. 



PAOi 



Introduction ............ 283 



Ciliary mechanisms producing the main food and respiratory current in Brachiopods 284 



Ciliary mechanisms on the gill-filaments and lophophore ..... 287 



The ciliation of the gill-filaments of Brachiopods ...... 293 



Summary of current-producing mechanisms and the mode of feeding in Brachiopods 294 



An explanation of some morphological characters in fossil and recent Brachiopods 295 

 Comparison of the ciliary mechanisms on the gills of Gastropods, Lamellibranchs, 



Amphioxus, and Brachioj^ods ......... 297 



The ciliary mechanisms on the gills of Cryptocephalous Polychsetes and on the 



lophophore of Phoronis . ...... ... 301 



The endostyle of Crepidula and Calyptraea ....... 303 



Comparison of the adaptations in Brachiopods and Lamellibranchs to the process 



of feeding ............ 307 



Summary ............. 308 



INTRODUCTION. 



The results of the writer's investigations on the cihary mechanisms on 

 the gills of Mollusca and Amphioxus (1 and 2) gave rise to the suggestion 

 that similar mechanisms might probably also occur in Brachiopods, for 

 it is a well-known fact that Brachiopods — like some Molluscs and Am- 

 phioxus — feed on the smaller organisms which are to be found floating 

 in the sea. Owing to the kindness of Dr. H. C. Williamson, of Aberdeen, 

 I have been able to examine living Crania which were obtained by dredg- 

 ing in Loch Fyne, and living Terebratula have also been obtained from 

 Naples. An investigation of the living gill-filaments — or lophophoral cirri, 

 as they are frequently termed in this group — showed that the ciliary 



