574 



Anatomy. "On the MetamorpJio.üa of Ampldoxus lanceohilns'. 



By Prof. J. W. VAN Wijhe. 



(Communicated in the meeting of April '^5, 1913). 



Anii»liioxiis slill continues to be one of the most interesting objects 

 for the moi-phology of vertebrates, though tlie time is past in which 

 he was almost considered as their ancestor. It is now pretty well 

 generally admitted, that Amphioxus is not the grandfather of 

 vertebrates. It lias appeared tliat his organisation deviates so strongly 

 fiom what must be regarded as tlie original type, that some morpho- 

 logists do not take him for a genuine grand-father, but for a ï:\q\)- 

 grand-father, who, in reality, does not belong at all to the family, 

 and only confuses its relations. 



There have been morphologists, and perhaps there are still some, 

 whose theories appeared to be so much at variance with the orga- 

 nisation of Amphioxus, that they have proposed to strike him out 

 from the group to which vertebrates belong, and if they had been 

 able would willingly have brought him back to the group of snails, 

 to which Pallas in his time supposed him to belong, and for that 

 reason gave him the name of Limax lanceolatus. 



Though these investigators could not deny, that Amphioxus is 

 aflined to vertebrates, in order to sa^-e their theories, they were 

 obliged to declare, that this relation is such a distant one, that it 

 is certainly not necessary to make allowance for his organisation. 



When however this organisation, both anatomically and embry- 

 ologically '), became better known, it appeared more and more 

 that Amphioxus shows indeed in many i-espects a very primitive 

 organisation, which must be taken as point of issue for that of the 

 higher vertebrates, whilst it presents, in other respects, such peculiai' 

 phenomena, that these must doubtlessly be regarded as deviations 

 from types, that are represented among vertebrates. 



I shall by-and-by discuss one of the most remarkable deviations. 

 It is the placing of the mouth and the gill-slits in the larva before 

 the metiimorphosis. 



1) How slowly our knowledge in this respect increases may appear from the 

 fact, that the celebrated morphologist Balfour was in 1882 still of opinion that 

 Amphioxus should possess no ventral nerve-roots, whilst, with regard to the 

 dorsal nerve-roots, one is still searching where the cells he, which, in vertebrates, 

 form the spinal ganglia. I have discovered under the atrial-epithelium that covers 

 the liver, the intestine and gut an enormously large number of splendid multipolar 

 ganglion-cells, whose axis-cylinder runs along the dorsal nerve-roots to the 

 spinal cord. 



