48 J. H. OETON. 



can pass is maintained by the test, and in Amphioxus by the expansion 

 of stout connective sheaths over the dorsal region of the pharynx held 

 in place by muscular attachments to the dorsal region of the body. 



The ciliation of the gill-bars of Balanoglossus is essentially the same 

 as that of Amphioxus. Hence the current of water through the body 

 of the animal is doubtless effected by the lateral cilia and a mode of food- 

 collection effected by the frontal cilia. 



Observations on late Ammocoete larvae indicate food-collection on the 

 gill-bars and the roof of the pharynx, as occurs in Amphioxus. An 

 attempt will be made to complete these observations. 



The mantle cavity of Solenomya togata is divided into inhalent and 

 exhalent chambers by the gill in the same way as in other Lamellibranchs, 

 namely, Anomia and Pecten. 



The ciliation of the gill of Solenomya closely resembles that of Nucula : 

 the lateral cilia produce the main current, the latero-frontal and the 

 frontal cilia collect food-particles, and the latter transport them to the 

 ventral surface of the gill, whence they are conducted forwards by 

 special transporting cilia towards the mouth to be eaten. 



Numerous small ciliated knobs occur on the ab-frontal face of the gill- 

 lamellse and serve to interlock with their fellows on opposite leaflets. 



These ciliated knobs correspond to the ciliated discs of the gill-filaments 

 of other Lamellibranchs, for example, the Mussel. 



Interlocking cilia occur on the edges of the upper and lower leaflets 

 of the gill and serve to lock the gill to the inner wall of the mantle, 

 and thus to partition the mantle cavity. 



The function of the Lamellibranch gill is probably mainly that of a 

 food collector and a water pump, and except in the Protobranchs is 

 probably not an organ in which aeration of the blood occurs. 



EEFERENCES. 



1. A. Willey. Amphioxus and the Ancestry of the Vertebrates. Mac- 



millan&Co. 1894. 



Feeding ofAnifhioxus, pp. 9, 39. Feeding ofAscidians, p. 185. 



2. A. Sedgwick. Student's Text Book of Zoology, Vol. II. London, 



1905, p. 22. 



3. Delage and Herouard. Traite de Zoologie concrete VIII. Pro- 



chordes p. 113, p. 144, Ascidians. 



4. H. Fol. Etudes sur les Appendiculaires du detroit de Messine. 



Mem. de la Societe de Phys. et d'hist. natiir. de Geneve. 

 T. xxi. 2. 1872. 



