ON THE STRUCTURE OF THE ANTENNAE. 585 



ever, I have not seen the organs themselves in the Ant, in which 

 Forel described them, I am unable to speak with any certainty 

 on the subject. 



The tympanules of Hicks and the simple pits of Krapelin 

 appear to me to be nothing more nor less than the open pore 

 canals left after the complete removal of the sensory setae ; 

 possibly closed by a thin plate of chitin, the result of the heal- 

 ing of the pore, after the sensory seta is shed. 



Setiferous sacs and canals are largely developed in the Mus- 

 cidae, and are typical in the Blow-fly. They were mistaken by 

 Graber for sacs containing otolith-like organs [270]. 



b. In the Blow-fly Imago. 



As has been already observed, I regard the antennas of the 

 Blow-fly as six-jointed, with a greatly-enlarged third joint a 

 view which was adopted by Robineau-Desvoidy, but one 

 which has met with little acceptance from entomologists. 

 This is due to the fact that the two basal joints of the three- 

 jointed bristle are so short that they are only seen with the 

 microscope. This organ is usually regarded as a mere seta. 



If the so-called bristle of the antenna is regarded as the 

 representative of the terminal joints of the organ, Leptis and 

 the Tachina exhibit a transitional condition, between the fili- 

 form antennae of the Nematocera and the sub-cylindrical 

 antennae of the majority of the Muscidae. In Leptis (Fig. 72, A) 

 there is a manifest enlargement of the first three joints without 

 any lateral projection of the third joint ; whilst in Tachina 

 (Fig. 72, B) the third joint is enlarged, but to a less degree 

 than in most Muscidae. 



Description of the Antenna in the Blow-Fly. The first joint of the 

 antenna is a narrow ring (Fig. 72, C, D, i), with several stiff setae on the 

 front of its distal margin. It articulates by syndesmosis, by its proximal 

 border with the torulus (see p. 122), and by its distal border with the 

 second joint of the antenna. 



The second joint (Fig. 72, C, D, 2) has the form of two irregular pyramids 

 placed base to base. The distal pyramid projects into a cavity at the 

 proximal extremity of the third joint, so that it is not seen externally. The 

 proximal pyramid is the largest ; it overhangs the proximal extremity of the 



