DEVELOPMENT OF THE ATUIAL CHAMBER IN AMPHIOXUS. 647 



Note on the Development of the Atrial Chamber 



in Amphioxus. 



By 

 E. Ray Lankester, M.A., L.L..D., F.R.S. 



Owing to the promotion of my friend Professor MacBride 

 to a post in the University of Montreal in Canada, it has not 

 been possible for me to confer with him personally as to the 

 significance of certain passages in his interesting and valuable 

 memoir on ''The Early Development of Amphioxus" published 

 in the present number of the Journal. I must therefore 

 take the passages in question as they standi and deal with 

 them in print. 



Professor MacBride has made the interesting discovery that 

 the lymph-canals in the metapleura of Amphioxus are pro- 

 longations of the pair of coelomic pouches which immediately 

 follow the head cavity (bifid in its later growth). He identifies 

 them with the collar cavities of Balanoglossus, and sees in 

 this relation a confirmation of the view, advanced originally 

 by Bateson, that the atrial chamber may be considered as 

 morphologically identical with the small region overhung by 

 the free posterior margin of the collar of Balanoglossus, and 

 the wall enclosing the atrial chamber with the free projecting 

 ring of the Balanoglossus collar. Whilst I by no means deny 

 that there is a relationship between the metapleura of Amphi- 

 oxus and the collar of Balanoglossus^ it appears to me that 

 MacBride has been led by theoretical bias into a serious 

 misapprehension of the significance of the observations on the 

 development of the atrial chamber in Amphioxus published 

 by me in conjunction with Dr. Arthur Willey in 1890. 



