AN AMPHIOXUS FEOM JAPAN. 105 



any other species. AVe know, unfortunately, very little of this B. Belcheri. 

 Giintlier counted 37. 14. 13-64 in specimens from Bornes and 37. 14. 14-65 

 in others from Prince of Wales Islands : the former thus agree more closely 

 with the Japanese form as far as these numbers are indications. The other 

 characteristics of B. Belcheri as given by gray and by Giinther do not add 

 very much to our knowledge of this species. The original description gray 

 in 1847, gives but a faint idea of the creature. He says it is very much like 

 Amphioxus lanceolatus, but thinks it more convex on the sides, with the 

 dorsal fin higher and with more numerous septa. In 1884 Giinther described 

 it as " very similar to but more more elongated than B. lanceolatuiii and the 

 fins instead of being dilated behind gradually decrease in width towards the 

 extremity of the tail." 



In the Japanese specimens, however, the fins are not like this but rather 

 markedly dilated. The dorsal fin is much more suddenly dilated at a point 

 vertically above the anus than in B. Icuiceolatum. The ventral fin is dilated 

 much as in some specimens of B. Icvnceolatum from Sicily. This dilatation 

 of the fins, however, can scarcely by relied upon as of much value to exclude 

 the Japanese specimens from the species of B. Belcheri, for in another 

 form, the B. californiense from Califorina, the tail fins present very different 

 amounts of expansion in different specimens preserved by different methods. 

 It may then be that the expanded fins are due to better methods of 

 preservation ; the specimens of B. Belcheri not being, in all probability, 

 prepared for histological study. 



As far as the evidence allows we may then, provisionally, decide that the 

 Japanese Amphioxus belongs to the species known as Brancliiostomuiit 

 Belcheri. The geographical distribution of species favors this conclusion 

 since we may easily suppose it extended from Bornes to Japan as it is 

 already known South to the Prince of AVales Islands and is thus of wide 

 disribution. 



In concluding that the lancelet of Japan is probably B ranch iostomum 

 Belcheri we can not Ijut emphasize the fat that the systematic knowledge of 

 this group is in a very unsatisfactory state and that a complete revision is 

 much to be desired ; in fact it is almost necessao'y before any permanent value 



