132 



H. NAKAGAWA. 



the variation is not in accordance with the size of the animal, because 

 one specimen of only 10£ mm. in length possessed 04 segments, while 

 another of 51 i mm. had only 62. 



As to the distribution of the segments into the three regions, it will 

 perhaps be proper to seek its normal state among the specimens that 

 possess the average number of segments. So by consulting the third 

 section of Table IV the two cases, 36, 17, 11 and 37, 17, 10, are ap- 

 parently most predominant, the former occurring 1G limes and the latter 

 11 times among 3G cases. Hence the formula for the present species is 

 36 (37), 17, 11 (10)— 64, 35. 



This does not apply to any of the nine species mentioned in E. A. 

 Andrews' paper*, but as I have at present no opportunity of examining 

 the specimens belonging to the species given there, I can not say 

 whether we have here a new species or whether it belongs to one of the 

 nine, which has not been collected and examined in sufficient number. 



August 17, 1897. 



Printed September 15, 1897. 



* An Amphioxus from Japan, Zool. Anz., Xo. 468. 



