64 ART. 4. N. YATSU : 



attached to them, yielding up the waste material by a process of 

 osmosis. It is certainly a fact that blood corpuscles are found 

 attached in numbers to the sheath (PL VI., Fig. 86). 



j. Otocysts. 1 



In the year 1860 Fritz Müller ('6o) found in the larva? 

 of Discinisca structures which he identified as organs of hearing. 

 These he found on both sides of the stomach just beneath the 

 dorsal valve and described them as " zwei ansehnliche Gehör- 

 bläschen von 0.04 mm. Durchmesser, in denen man 20-30 Oto- 

 lithen (von etwa 0.002 mm.) in lebhafter tanzender Bewegung 

 erblickt" (p. 77). 



In his next paper ('6i) on the Discinisca larvœ, he discusses 

 the changes in the soft parts and states : " the previously 

 spherical auditory vesicles were shrunken into longish sacs, closely 

 surrounding otoliths. In somewhat older animals there were no 

 traces of the organ of sense " (p. 56o). 



Morse ('8i) made observations on Japanese Lingula and 

 discovered the auditory capsules. From the abstract of his paper 

 read before a meeting of the Boston Society of Natural History, 

 I can only learn that " their [otocysts] position and general 

 appearance recall the auditory capsules as figured by Claparède 

 in certain tubicolous Annelids " (p. 157). This is the only 

 description hitherto published of the presence of the otocysts in 

 the adult Brachiopods. 



In the same year Brooks ('78) studying Lingula-larvœ 



1. In the present section I have employed the term "otocyst" from the anatomical 

 similarity to the organ of the same name found in other animals, not from the physiolo- 

 gical point of view. The vesicles must, I believe, subserve as an organ of stability as 

 ascertained in other cr.ses by Vves Delage, Engelmann, Yerworn, Beer, etc. 



