178 SELECTED NOTES. 



pair of nerves is the largest in the thorax and crosses to the oppo- 

 site sides immediately on entering the ganglia. The pedicel is a 

 hollow tube connecting the base of haltere with the globe. On 

 the external surface it is covered with hairs ; the interior is divided 

 by a septum, which is continued the whole length of the pedicel ; 

 a large tracheal vessel passes through it to the globe, where it 

 breaks up into many branches, which ramify in the tissue. I have 

 not been able to trace any more in it. 



Sarcophaga carnaria, longitudinal sections of haltere.— 



These show the vascular tissue in the so-called globe of the haltere 

 (see Fig. 5). In all the halteres I have examined the deep invagi- 

 nation seen in these sections of the globe is invariably present, and 

 there is always a mass of connective tissue extending from the 

 invaginated wall to the opposite wall of the globe. The purpose 

 of the invagination I do not know, unless by some means it allows 

 of a certain amount of expansion and contraction of the globe. 

 The large glands most probably secrete a fluid necessary for organs 

 at the base of the haltere. 



The halteres of diptera doubtless assist in their locomotion, 

 but the evidence of their elaborate structure proves that they have 

 another most important function. The position of the papillae is 

 such as to present a front in every direction, and their structure is 

 so delicate as to permit vibration when sound-waves or other 

 movements of the air impinge upon them. The nerve epithelium, 

 bathed in fluid which is secreted in the globe, together with the 

 very rich nerve-supply, also point to their being rudimentary audi- 

 tory organs. Otoliths, so commonly found in the Crustacea and 

 Mollusca, I have not met with here, but it is no proof that they 

 do not exist. 



The great number of papillae (four hundred to five hundred) in 

 each haltere, and the small number of olfactory organs (two in 

 each antennae) found in many flies which feed on the nectar of 

 flowers, compared with M. vomitoria and M. domesttca, whose hal- 

 teres carry half the number of papillae, and in whom the olfactory 

 sense is highly developed, show that the former possess an acute 

 sense to warn them of danger when their heads are buried in the 

 blossoms of the plants they frequent, and that the latter have 

 comparatively little use for such a sense. 



