Gastropoda 



LamelUbranchia 



Type A 



Type B 



Ic 

 ab.f.c. 



Protochordata 



Brachiopoda 



f.c. 

 l.f.c. 



ab.f.c. 



g.s. 



Fig. 9. — Transverse sections of the gill-filaments of members of Gastropods, Lamelli- 

 branchs, Protochordata, and Brachiopods, illustrating the essential similarity of 

 the ciliation of the filaments in all these groups. (Variously magnified.) 

 I.e. Lateral cilia which produce the main food and respiratory current in all 



the groups. 

 Frontal cilia which are the main food -collecting cilia in all the groups. 

 Latero-frontal cilia, which are special food-catching cilia present only in 

 some Lamellibranchs, as Nucula, Anomia, Mytilus, Cardium, and 

 others ; they lash in the direction shown by the adjoining arrows. 

 Ab-frontal cilia present and well developed in Gastropods and some 

 Lamellibranchs, but less well developed in Amphioxus and Ascidians ; 

 absent in Brachiopods. These cilia assist both in food -collection and 

 in producing the main current. 

 Internal supports for the gill-filaments and present in all the groups, but 

 additional support by calcareous spicules is given in some Brachio- 

 pods, as in Terebratula vitrea, shown in the Brachiopod section B. 

 Tn the above types of gill-filaments Gastropods are represented by a transverse 

 section of a filament of Crepiduln fornicata ; Lamellibranchs by two sections repre- 

 senting the two types of ciliation in this group. Type A is of Ghjcimeris glycirneris, 

 and would serve equally well for Pecten, Area, and others. Type B is of M}jtilus 

 edulis, and represents Nucula, Solenomya, Anomia. Cardium, Ostrea, Anodon, 

 and many others. Protochordata are represented by a section of a secondary gill- 

 filament of AmpJuoxus lanceolalus, but sections of Ascidian and Enteropneustan 

 (as represented by Ptychodera) gill-filaments are essentially similar to that of 

 Amphioxus in their ciliation. 



The two kinds of filaments present in Brachiopods are represented by the 

 Brachiopod sections A and B. The section A is of a ventral filament of Crania 

 avomala, and B is of a dorsal filament of Terebratula vitrea. The latter section is 

 slightly idealized in that the su])porting spicules present within the chitinous gill- 

 support are represented in the drawing although dissolved out of the actual section 

 bv the fixative. 



