DEVELOPMENT OF ATRIAL GHAMBEE OF AMPHIOXUS. 445 



The Development of the Atrial Chamber of 

 Amphioxus. 



By 

 E. Ray I<ankester, H.A., Iili.]>., F.R.S., 



and 



Artbur IVilley, 



Student of University College, 



With Plates XXIX, XXX, XXXI, XXXII. 



Last year one of us (Mr. Willey) collected during the months 

 of May, July^ and August many hundreds of embryos and 

 larvse of Amphioxus in Sicily. 



The material so obtained has been worked out in the labora- 

 tory of University College. The period of the development^ 

 to which we determined first of all to give attention^ was that 

 before which Hatschek^s well-known work stops short. Series 

 of sections were prepared in order to ascertain the mode in 

 which the atrial chamber takes its origin and the subsequent 

 history of the gill- slits, viz. as to how the slits on the left side 

 of the pharynx originate. The relation of the larval to the 

 adult mouth and the details of the curious process of move- 

 ment of the mouth from a unilateral to a median position were 

 included in the scope of our inquiries. 



Amphioxus occurs in great numbers in a comparatively 

 small lakcj or pant an o, which is situated behind, and sepa- 

 rated from the sea by, the village of Faro, near Messina. It 



VOL. XXXI, PART III. — NEW SER. G G 



