40 AKT. 4. — N. YATSU : 



«hall deal with them together so as not to interrupt the course 

 of description. 



a. Habits. 



The free-swimming larvae of Lingula occur abundantly in the 

 plankton collected in the inlet of Moroiso just in front of the 

 Marine Station at Misaki. They are taken with tow-nets from 

 the latter part of July until the first half of September i.e. during 

 about two months. On rainy or windy days, however, they arc 

 invariably absent, since doubtless they sink to the deeper water. 

 More of them are collected at rising than at ebb tide. This fact 

 coupled Avith another, viz., that stages earlier than the 7 p. c. 

 stage are seldom met with, make it possible that the embryos 

 are carried out of the bay at very early stages, and it is only on 

 their return to the region of the mud flats, that they are taken 

 by the collector. The larvse are captured at the surface as well 

 as at the depth of a few feet. But how deep they can sink, 

 and how far off the shore they are carried, I have not yet tried 

 to determine. 



The larvse do not move about to any great extent among 

 the plankton collected with a tow-net, and are generally found 

 quite immobile in the bottom sediments which are composed of 

 Radiolarians, Diatoms, etc. Taking advantage of this peculiarity 

 I generally obtained the larvse by searching for them only in 

 such sediments. After they with a small quantity of water have 

 been transferred to a slide the only movements I have noted are 

 occasional contractions of the arm-apparatus, by which the body 

 cavity is dilated. It may be noted that the arm-apparatus con- 

 tracts suddenly, and then again slowly extends until it fills up 



