Objects for the Microscope. 143 



arranged in rows. The upper group is in spiral lines, the 

 lower is on a broad flat surface, and only on one side. 

 Each vesicle is a small sac, filled with fluid, and over- 

 arched by a protecting hair, and when a good side view is 

 obtained they are seen to be quite spherical. 



The two naturalists, Dr. Hicks and Mr. Purkiss, who 

 have noticed these organs, suppose them to be olfactory 

 vesicles. There is a very large nerve given off from the 

 great thoracic ganglion into the halteres, larger even than 

 those branches which pass into the wings and legs of flies, 

 which makes it very likely that in these very small appen- 

 dages lies a great sensitiveness of some kind. No less than 

 360 of these vesicles are found in the halteres of Rhingia ; 

 and for what purpose ? 



Dr. Hicks justly remarks, that it is scarcely for hearing, 

 as they are so near the buzz of the wings, and them- 

 selves in constant motion, so that other sounds would be 

 drowned ; but that the current of air produced by this very 

 fluttering, and also the position of the halteres near the 

 largest thoracic spiracle, make it extremely probable that 

 they receive the floating odours in the air, and communicate 

 them to the brain, or cephalic ganglion, directing thus the 

 Blow-fly to the carrion, the Rhingia to the flowers. 



HALTERES OF TABANUS. 



" These are very similar to those of the Rhingia, with 

 the addition of seven vesicles on the shaft of the halteres 

 to the upper part of the facet of the ridge, and another 

 group of eight or nine beneath the ridge opposite the 

 boarder facet."* 



The shaft of the halteres is tubular, and is the channel 

 for the branch of the nerve which passes up and expands 

 in the head. 



The head of the halteres contains cellular substance ; 

 there is also a groove on one side lined with a very delicate 

 membrane, and beneath which there is a group of hairs. 



* See ' Journal of the Proceedings of the Linnaean Society of London,' 

 November, 1856. 



