ON THE DEVELOPMENT OF LINGULA ANATINA. 65 



confirmed Müller's observations. In the larvae of the close of 

 the 7 p. c. stage, he saw on the dorsal side that nerve fibres 

 turn backwards from the ventral side, and " terminate in a pair 

 of large dilatations, * * each of which contains an elliptical cavity, 

 within which are numerous vibrating otoliths " (p. 63). On the 

 fate of the otocysts he adds : "if the otocysts had been present 

 [in the sedentary larva?], and no larger than those of the latter 

 figure [10 p. c. stage], they would not have been visible with any 

 available magnifying power. There is no reason, therefore, to 

 suppose that they disappear during development " (p. 64). 



Just twenty years later Blochmann ('98) found the auditory 

 vesicles discovered by Fritz Müller in the larvae of Discinisca, 

 but he considered them nephridial funnels. " Sie liegen dicht 

 unter der Dorsalschale und wenden ihre erweiterte Oeffnung 

 dorsalwärts. Den Anfang ihres Ausführungsgangs sieht man leicht 

 (Fig. 1). An einem Exemplar konnte ich diesen bis zu seiner 

 Mündung an der Vorderwand verfolgen. Er verläuft zwischen 

 den Oc. anterior und dem lateralis. Die 20-30 Körnchen, die 

 Fritz Müller für otolithen hielt, waren jedenfalls nicht weiter 

 als Exkretionskörnchen, die durch die Wimpern des Trichters in 

 Bewegung gehalten werden. Ich kann auch die von Brooks für 

 die Lingula-\'AY\ r e beschriebenen Otocysten nicht als solche an- 

 erkennen " (p. 422). In his "Untersuchungen über den Bau 



der Brachiopoden (Zweiter theil) " ('oo) he advances the same 

 view as in his former paper (p. 124). 



If we examine the detailed structure of these vesicles in the 

 larvae of Lingida, I think, we can safely conclude with Fritz 

 Müller and Brooks that they must be regarded as the otocysts. 

 In the dorsal view of living larvae older than the 5 p. c. stage we 

 can readily see a pair of very conspicuous vesicles (ot.) posterior 



