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 Muscidse 

 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. 



FIG. 84. One of the lobes of the prosternal orcjan seen in section ; b, basilar plate 

 of the head ; c, cervical sclerite ; con, condyle ; n, nerve ; / th t 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 setae (PL VIII. 

 Fig- 3, 6), beneath which there is a layer of large ganglion 

 cells, connected with a branch of the prothoracic dorsal 

 nerve. 



