58 



An examination of sections of some of the above six specimens 

 sent from Japan shows that they agree closely in their general anatomy 

 with the common Amphioxus of Europe, the form known as Branchio- 

 stotnum lanceolatum. Though thus agreeing in internal structure and 

 presenting no new anatomical aspects of interest as far as observed 

 they differ in external characters and are undoubtedly specifically 

 distinct. The general outlines and proportions of the body and fins, 

 the number and arrangement of the muscle segments, which deter- 

 mines the relative positions of anus and atriopore , and length of tail 

 are the characters commonly regarded as of systematic value and it 

 is in these that the Japanese form does not agree with the Euro- 

 pean. 



Upon such characters a number of more and less satisfactory spe- 

 cies have been based, often enough from dead specimens poorly pre- 

 served. Accepting these for the present, in the absence of better, we 

 may summarize the characters of the lancelets thus far described by 

 means of the following table. 



1) Branchiostomum lanceolatum 36-14 



2) » caribaeum 35-14 



3) » cultellum 32-11 



4) » hassanum 44-14 



5) » Belcheri 37-14 



6) » elongatum 49-18 



7) » californiense 44-16 



8) » pelagicum 36? • 16? 



9) Asymmetron lucayanum 44 • 9 

 In this table the first column of figures indicates the number of 



muscle segments anterior to the atriopore ; the second the number be- 

 tween the atriopore and the anus; the third the number posterior to 

 the anus, that is in the tail. These three colums thus serve to indicate 

 the relative lengths of the three main divisions of the body as well as 

 to state the actual number of segments in each; from them we may 

 judge what the general aspect of a species will be , whether with a 

 short tail , a long trunk or with closely approximated atrial and anal 

 openings etc. The fourth column represents the average number in 

 the entire animal: it is not always the sum of the preceeding three 

 columns though it would be so in any particular animal. The last 

 column gives the entire length, on the average. 



The six lancelets from Japan have each sixty-four segments, of 



12—61. 43 mm 



9—58. 43 » 



10—52. 23 » 



17—75. — » 



14—65. 65 » 



12—79. 60 » 



9—68. 70 » 



15—67. 10 )) 



13—66. 13 » 



The probabilities are therefore that the lancelet is found in all favorable localities 

 in the southern part of Japan. (Aug. 1894. K. Mitsukuri.) 



