NO. 8 MORPHOLOGY OF INSECT SENSE ORGANS SNODGRASS 



45 



on the antennae of some Diptera ; those of the housefly are described 

 by Rohler (1906). Some of the cavities contain a single group of 

 from 10 to 20 pegs; others are compound, the cavities being divided 

 into shallow compartments, each with its group of pegs. These or- 

 gans were called " otocysts " by Graber, but Rohler regards them as 

 olfactory in function. The labial palpus of the cabbage butterfly 

 (Picris) also has at the tip a deep cavity containing many sense pegs. 



SENSILLA AMPULLACEA 



This term is given to sense organs of the sunken peg type in which 

 the cuticular cavity is deeper and more flask-like (fig. 19 C) than 



F1 



A 



Fig. 19. — The cuticular parts of several varieties of sensilla coeloco- 

 nica (A, B) and ampullacea (C, D). 



A, simple pit peg with thick chitinous walls. B, thin-walled peg more 

 deeply sunken into cuticular cavity. C, a flask-shaped organ. D, a 

 Forel's flask with long tubular neck. 



in the typical sensilla coeloconica. In some, the " flask " is far re- 

 moved from the surface and is connected with the outer cuticula 

 by a long, tubular neck (D). Organs of this kind are known as 

 Forel's flasks. Sensilla ampullacea are particularly characteristic of 

 the antennae of Hymenoptera. They are usually regarded as organs 

 of smell. 



V. THE CAMPANIFORM ORGANS 



The sense organs grouped in this class are clearly related to one 

 another structurally. They are all, however, of such simple form 

 and yet vary so much in shape, that they present no feature on which 

 a descriptive or a distinctive name can be based. They have been 

 called resides, organs of Hicks, papillce, cupola organs, dome organs, 

 wnhrella organs, hell organs, and sense " pores." Since the external 

 part commonly has the shape of a thin-walled dome or bell, or sug- 

 gests that it has been derived from such a form, the name campani- 



