Zoology. — "On the Anatomy of the Larva of Am])hio^us lanceolatus 

 and the Explanation of its Asymmetn/'. By Prof. J. W. 



VAN WlJHE. 



(Communicated in the meeting of November BO, 1918). 



P'or many years I have attempted to complete a part of tlie 

 many lacunae in onr knowledge of the morphology of Amphioxus, 

 hecanse this morpliology is in many respects the basis for the com- 

 parative anatomy and embryology of the Vertebrates. 



After the publication in 1914 in the Transactions of this Academy 

 of ray work on the changes of the larva of Amphioxus during the 

 metamorphosis, during which growth ceases, 1 have managed to 

 obtain sufticieut mateiial to investigate the larva during the growth- 

 period. Now that the research and the necessary drawings have 

 been completed — the text must still be written — I shall here 

 discuss some results. 



Many years ago (1893) I fonnd that the mouth of Amphioxus was 

 only apparently placed niore or less symmetricalfy, that in fact however 

 it lies exclusively on the left side as the nerves and muscles of the 

 buccal cavity withont exception belong to the left side of the body, 

 which was later on confirmed by others. This fact is in accordaiu-e 

 with the earlier discovery of Kowalevsky (1867) that the buccal 

 opening in the larva of Amphioxus is situated, not mesially, but on 

 the left side of the fore-end of the body. 



Through its mouth, which is a mesial organ in all the other 

 Metazoa, Amphioxns and undoubtedly also tiie related genus Asym- 

 raetron') stand isolated as remarkable in the whole animal kingdom. 



It has been repeatedly attempted to declare the mouth of Amphi- 

 oxus for a mesial organ by accepting that it has removed to the 

 left side. Its occurrence in the larva on that side had then to be taken 

 up as an abbreviation of development. This lemoval would then be 

 analogous to the phenomenon observed in the eye of the Plenro- 

 nectidae. The young larva of the flat-lishes has an eye on each side 



') Tattersall (Notes on the Classification and geographical Distribution of the 

 Gephalochorda. Proceedings and Transactions of the Liverpool Biological Society, 

 Vol. 17, 1903) has shown that in the Homomeria (Acrania) we can distinguish 

 only these two genera: .'\mphioxus (Branchiosloma) and Asymmetron. 



