308 J. H. OKTON. 



siphonate forms in Lamellibranchs is probably represented by members 

 of those genera in which the postero-lateral angles of the shell are very 

 much drawn out, as in Productus giganteus, Sfirifer verneuilli, and species 

 of Lepteena and Platystrophia, and in other forms common in the 

 Rhynchonellidae, in which the front middle part of the shell is differ- 

 entiated from the rest in such a way as to resemble a siphon (see Fig. 8, C, 

 p. 296). In all these forms it is highly probable that the shell modifications 

 are correlated with localization of the food-currents. Lingula, however, 

 has been shown by Morse (7) to dispose the mantle setse in such a way 

 that they form a sort of temporary siphon for the ingoing and the out- 

 going currents, and this method of forming siphons may occur in other 

 Brachiopods. 



From the description of the Brachiopod lophophore given in the pre- 

 ceding pages there can remain no doubt that that organ is analogous 

 to the gill of Lamellibranchs, as has indeed already been observed by 

 Lankester (12). The resemblance in appearance of the lophophore to 

 the palp of a Lamellibranch such as Nucula is indeed close, but that 

 the resemblance is superficial will have been seen from the foregoing 

 account of its function. Hence, if the organs can be compared at all 

 Morse is undoubtedly wrong in comparing the lophophore as he does (13) 

 with the Lamellibranch palp. Thus it is seen that on the whole the parallel 

 developments of organs in the Brachiopods and Lamellibranchs are 

 much fewer than might have been expected from the similarity in their 

 mode of feeding, and the differences which do exist may probably be 

 very largely due to the absence in Brachiopods of that consolidation of 

 the gill-filaments which appears to have played such an important part 

 in the evolution of the Lamellibranchs. 



SUMMARY. 



Brachiopods feed in the same way as some Gastropods, as, for example, 

 Crepidula, most Lamellibranchs, Amphioxus, and Ascidians, that is, by 

 establishing a current of water through certain spaces bounded by the 

 body, and sieving off the food-particles contained in that current by 

 means of the lophophore and its cirri. 



The cilia on the gill-filaments (cirri) are differentiated in Brachiopods 

 into lateral and frontal cilia, in essentially the same way and with the 

 same functions as in some Gastropods, most Lamellibranchs, Amphioxus, 

 Balanogiossus, and some Ascidians. 



The main current through the mantle cavity in Brachiopods is pro- 



