WERNER MARCHAND 29 



Special Anatomy of Tabanid Larva. Graher's Organ. 



Almost the only detail of the structure of tabanid larvae which has 

 been studied more extensively is a peculiar organ situated on the 

 dorsal side of the segment before the last, and discovered first by 

 Graber (1878), who, while conceding that it has very little resem- 

 blance to an auditory organ, nevertheless may have to be placed in 

 this category. As the situation of the organ is rather unusual if it is 

 auditory, Graber recalls the discovery by Grobben of similarly situ- 

 ated organs in the larva of another fly, Ptychoptera contaminata 

 (Tipulidae), and of which the auditory function seems fairly certain. 

 Whether similar organs are found in other dipterous larvae is not 

 known; Malloch (1917) does not mention them. The organs seem to 

 occur in all tabanid larvae, but to be more easily seen in the young 

 stages; they have been overlooked by some later investigators, nota- 

 bly Hart (1895) and Hine (1901-06), but have been seen and figured 

 by Walton (1908) for Goniops chrysocoma (only as dots), and by 

 Mitzmain (1913) for Tahanus striatus, all of whom have apparently 

 overlooked the European literature on the subject, Mitzmain assum- 

 ing that the organ must either be peculiar to the larvae observed 

 by him, or have been overlooked by the previous authors. 



Graber found the organs in the abdomen of the larva, at the 

 sides of the two last segments. They consist of a cornea-like infla- 

 tion of the integument which is covered inside with its epithelium. 

 The open inner side of this vesicular invagination seems to be closed 

 by a membrane supported by radial elastic fibers, the fundus of which 

 can be extended by means of a strong muscle. According to Graber, 

 the presence of a special nerve, which, however, approaches the 

 vesicle without any specialized termination, is proof that we are 

 dealing with a sense organ. 



However, what characterizes them as auditory organs are two or 

 three otolith-like bodies found in the liquid contents of the capsule. 

 These abdominal otocysts consequently differ from antennal structures 

 described elsewhere by Graber, first, by belonging to the integument 

 itself, second, by their inner wall not being formed by chitin but by 

 the epithelium. As a consequence of this, the development of cuticu- 

 lar auditory hairs is naturally also suppressed, and a new type of 



