OX THE DEVELOPMENT OF LINGULA AXATIXA. 107 



larvae of Lingula. Otoliths were also observed crowded together 

 at the centre of the otocyst. The tentacle is not so cirrus-like 

 as in Lingula and ends in a knob (PL VI., Fig. 90 a). Ven- 

 trally and a little posteriorly to the knob a very deep furrow 

 passes posteriorly and stops short near the mouth. From the 

 ventral margin of the knob a protuberance hangs over the furrow. 



The position of the specimen in swimming suggests the figure 

 by Fritz Müller, but the neck region was not so long as in 

 his figure, and the proportion and length of the tentacle and 

 cirri were somewhat different. 



Curiously enough all larvae of Discina hitherto studied 1 are 

 exactly at the same stage ' i.e. the 4 p. c. stage. And there 

 evidently must be some reason to account for this. It is possible 

 that in Discina the free-swimming larvae at a particular stage 

 (the 4 p. c. stage), that is at a period shortly before the fixation, 

 make their way toward the coast, as the Ling ula-hr vue at the 

 7-9 p. c. stage. 



Zoological Laboratory, 

 Tokyo Imperial University. 

 Besinnins; of 



October, 1901. 



1. The specimens Mokse has studied ('70) must certainly have been much older than 

 the 4 p. c. stage. 



