310 J. H. ORTON. 



serves the same purpose, that is, it secretes mucus which is passed on 

 to the gills for the entrapping and the transportation of food-particles. 

 On the right side of the endostyle of Crepidula is a ciliated groove, 

 which carries mucus and some food-particles forwards to serve for 

 catching and expelling the heavier food-particles which enter the front 

 portion of the inhalent chamber. 



The independent origin of essentially the same ciliary mechanisms in 

 Molluscs, Protochordata, Brachiopods and some Polychaetes, and of a 

 similar glandular organ, the endostyle in Crepidula and Amphioxus and 

 Ascidians, are facts which add greatly to the difficulty of determining with 

 any certainty what are homologous organs in different animals. It also 

 follows that similar organs occurring in different animals and having the 

 same function are never necessarily homologous. 



The adaptation in Brachiopods and Lamellibranchs to the process of 

 feeding are compared, and the suggestion is made that the present 

 decadent condition of the former group is due to the absence of that 

 consolidation of the gill and correlated modification of the mantle which 

 appear to have conduced to the present relatively flourishing condition 

 of the Lamellibranchs. 



EEFERENCES. 



1. J. H. Orton. The Mode of Feeding in Crepidula, with an account of 



the current-producing mechanism in the mantle cavity, and some 

 remarks on the mode of feeding in Gastropods and Lamellibranchs. 

 Journ. M.B.A. Vol. 9, No. 3. 1912. 



2. J. H. Orton. The Ciliary Mechanisms on the Gill and the Mode of 



Feeding in Amphioxus, Ascidians, and Solenomya togata. Journ. 

 M.B.A. Vol. 10, No. 1. 1913. 



3. J. Herouard. Sur les Courants de Nutrition des Brachiopods. Journ. 



de Conchyliologie, Paris. 3 Ser., Tome 17. 1877. 



4. A. E. Shipley. On the Structure and Development of Argiope. IMittheil. 



Zool. Sta. Neapel. IV. 1883. 



5. A. E. Shipley. Molluscs and Brachiopods. Cambridge Nat. Hist. 



Vol. 3, pp. 463-488. 1895. 



6. J. F. Van Bemmelen. Untersuchungen fiber den Anatomischen vmd 



Histologischen Bau der Brachiopoda Testicardinia. Zeit. fur 

 Naturwissenschaft. Jena. XVI, N.F. IX, 1, 2. 1883. 



7. E. S. Morse. On Japanese Lingula and Shell Mounds. Amer. Journ. 



of Science and Arts. Series 3, Vol. 15, p. 157. 1878. 



