ON THE STRUCTURE OF THE ANTENNZ. 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 Krdapelin 
appear to me to be nothing more nor less than the open pore 
canals left after the complete removal of the sensory sete; 
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- 
cide, 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 antenne 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 antennze of the Nematocera and the _ sub-cylindrical 
antenne of the majority of the Muscide. 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 Muscide. 
Description of the Antenna in the Blow-Fly.—The first joint of the 
antenna is a narrow ring (Fig. 72, C, D, 1), 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 
