THE PROSTERNAL ORGAN. 633 
sucker are, however, very highly developed, and are unusually 
large (Fig. 83). I have been quite unable to find any organs 
which can be regarded as special nerve-terminals, either on 
the ligula or in the interior of the mouth. I believe, as com- 
pared with the Hymenoptera, the power of taste in the Muscidze 
is much less highly developed. 
16. THE PROSTERNAL ORGAN. 
Allusion has already been made to the prosternal organ 
(p. 179). This is one of the most incomprehensible structures, 
having the characters of a sensory organ. I ventured to suggest 
that it is concerned in registering, as it were, the movements of 
the head and fore-limbs, but with the further knowledge of this 
structure which I now possess, I entertain the gravest doubts 
of the possibility of such an explanation of its function. 
Fic. 84.—One of the lobes of the prosternal organ seen in section ; 4, basilar plate 
of the head ; c, cervical sclerite ; con, condyle ; , nerve ; p th, part of the pro- 
thorax. 
Although I drew attention to it in my former work [62] in 
1870, it does not seem to have attracted any attention since, 
neither have I found any description of a similar organ in any 
other insect. 
This structure lies in a deep cavity between the basilar plate 
of the head and the manubrium (Fig. 84), on either side, and 
consists of a plate covered with long fine sete (Pl. VIII. 
Fig. 3, 6), beneath which there is a layer of large ganglion 
cells, connected with a branch of the prothoracic dorsal 
nerve. 
