WERNER MARCH AND 35 



not containing pigmented bodies. Henneguy is inclined to place the 

 organ among the chordotonal organs. 



Lecaillon, having in 1904 sent some larvae of Tabanus quatuorno- 

 tatus to Henneguy, studied the organ at the latter's suggestion. He 

 records a number of facts which may facilitate further research on 

 the subject. The principal results of his observations are as follows: 



1. Graber's organ exists in all larvae of Tabanus quatuornotatiis. It should 

 consequently be sought for among the tabanids, and possibly also in related 

 families. 



2. It already exists in the larvae hatching from eggs, but it continues to de- 

 velop as the larvae grow. 



3. In very young larvas its structure corresponds to that described by Henne- 

 guy; in fact he made his observations on very young larvae. 



4. As the larvae grow, the primitive structure becomes more complicated and 

 more closely resembles the structure described by Graber. This author ob- 

 served full grown larvas. 



5. Consequently it can be stated that Henneguy 's description applies to the 

 young condition of the organ, and that of Graber to the fully developed condition. 



6. In Lecaillon's observations, as shown by the figures, the pigmented bodies 

 do not always remain regularly arranged in pairs, contrary to Graber's descrip- 

 tion. They are seen frequently placed one behind the other in the posterior duct 

 of the organs. Sometimes there is an odd number of them in this duct, which 

 means undoubtedly that these granules can sometimes be discharged or expelled. 



7. While nothing can be said with certainty about the function of Graber's 

 organ, Lecaillon considers it glandular in nature rather than a sense organ. 



The figure of the larva given by Lecaillon (Plate 10, Fig. 117) was 

 obtained from a living larva of Tabanus quatuornotatus one month 

 old, seen in dorsal aspect with light falling through, a larva at this 

 stage being still very small. Two other figures (Plate 10, Figs. 118 

 and 119) give the aboral extremity of two other larvae slightly older 

 than the first one. 



As seen in these figures, the main part of the organ of Graber oc- 

 cupies the median and dorsal region of the next to the last segment, in 

 almost its entire length, and is situated not far from the two large 

 tracheal trunks, which open, one near the other, at the end of the last 

 abdominal segment. It consists mainly of an oval sac or cyst pro- 

 longed posteriorly into a tube. The oval and dilated part is subdi- 

 vided by a septum in two cysts placed one behind the other. Careful 



