284 J. H. ORTON. 



mechani'sms on these filaments are essentially the same as those occurring 

 on the gill-filaments of Amphioxus, Lamellibranchs, some Gastropods, 

 and most Ascidians. As it was found that existing accounts of the 

 mode of feeding in Brachiopods are vague and incomplete the following 

 description of the process has been written. 



The nutritive currents in Brachiopods were the subject of an investi- 

 gation by J. Herouard (3) as early as 1877. This writer conceived the 

 ingenious plan of investigating these currents by constructing artificial 

 lophophores of lead piping perforated in places corresponding to the 

 point of attachment of the filaments. It was assumed that a representa- 

 tion of the action of the tentacles would be obtained by squirting water 

 under pressure through the holes in the artificial lophophore. Unfortu- 

 nately, examination of the living filaments shows at once that this 

 assumption is wrong, and that the experiments consequently were 

 valueless. The gills of Brachiopods have, however, been investigated 

 more recently by Shipley, who described the gill-filaments of Argiope 

 as having cilia on three of their four sides, and figures these cilia as being 

 all similar (see 4, Plate 39, Fig. 13). Later, Shipley (5) states that in 

 Brachiopods " the cilia which clothe the tentacles (i.e. gill-filaments or 

 cirri) keep up a constant flow of water into the mantle cavity. This 

 stream not only serves to aerate the blood of the animals — a process 

 which probably takes place through the thin inner lining of the mantle 

 — but it also brings with it a number of diatoms and other minute 

 organisms which serve as food. These particles become entangled in the 

 tentacles, and are ultimately lodged in the groove at their base, and 

 passing along this by the action of the cilia they find their way into the 

 wide mouth, into which the groove deepens in the posterior median 

 line." It will thus be seen that the manner in which the chief food- 

 current is produced and the differentiation of gill-cilia noted in the 

 following pages have not been described. Moreover, it will be shown 

 here that there exist in various parts of the body other ciliary mechanisms 

 than those on the gill, which play an important part in the process of 

 feeding. 



CILIAEY MECHANISMS PEODUCING THE MAIN FOOD AND 

 EESPIBATOEY CUEEENT IN BEACHIOPODS. 



Brachiopods — like Amphioxus, some Molluscs, and other animals — 

 obtain their food by maintaining a continuous current of water through 

 a cavity enclosed by portions of the body, and capturing the organisms 



