288 



J. H. ORTON. 



shown in Fig. 7, p. 292, and in the lateral view of a living filament shown in 

 Fig. 3. From these figures it is seen that the cilia are differentiated 

 into three rows, one extending along that face of the filament which 

 faces the incoming current, and two extending either along the sides of 

 the filaments or along the edges of the filam.ents at the sides of the former 

 row. Those rows of cilia on the face of the filament facing the incoming 

 current may be called frontal cilia in comparison with the similar cilia 



Fig. 4. — Diagram of the currents present in the mantle cavity of a Brachiopod as repre- 

 sented by Crania. 



The diagram i-epresents a section taken on one side of the median antero- 

 posterior axis through the shell and the whorls of the lophophore. One anterior 

 and one posterior occlusor muscle are shown. 



The larger arrows indicate the course of the main current through the mantle 

 cavity. The large arrow whose head ends above the letter A indicates the course 

 of the ingoing current and the one beginning below B that of the outgoing current- 

 The three arrows between and to the right of A and B indicate the course of the 

 current through the gill-filaments on the lophophore. The dotted arrows on 

 either side of A indicate the region where the heavier food-particles fall out of 

 the main stream on to the mantle and are expelled by the mantle cilia as indicated 

 by the long dotted arrow placed parallel to the lower mantle. The direction 

 in which the cilia lash on the dorsal mantle is sho\^Ti by the dotted arrow along- 

 side it. The small dotted arrows on the lophophore and gill-filaments show the 

 course of the food-collecting streams. 



A. Inhalent chamber of one side. 



B. Exhalent chamber of one side. 



described in Molluscs and Amphioxus (see 1 and 2), while the rows of 

 cilia on the sides of the filaments may be similarly called lateral cilia. 

 Thus the faces of the filaments may be termed respectively frontal, 

 lateral, and ab-frontal, the latter being the face opposite the frontal. 

 The lateral cilia (well shown in Figs. 3 and 7 I.e.) are the chief pro- 

 ducers of the main food and respiratory current in Brachiopods. They 

 lash across the length of the filament, as shown in Fig. 3, from the lower 

 portion of the mantle cavity to the upper. The origin of the lophophore 



