THE INTERNAL ANATOMY OF INSECTS 



155 



a b 



Fig. 175. — Sense-domes (From Berlese). 



The sense-domes are found in various situations, but they occur 

 chiefly on the bases of the wings and on the legs. Each sense-dome 

 consists of a thin, hemispherical or more nearly spherical membrane, 



which either projects from the 

 outer end of a pore in the 

 cuticula (Fig. 175, a) or is 

 more or less deeply enclosed 

 in such a pore (Fig. 175, h)\ 

 intergrades between the two 

 types represented in the accom- 

 panying figures occur. 



When a sense-dome is 

 viewed in section a nerve- 

 ending is seen to be connected 

 with the dome-shaped or bell- 

 like membrane. A striking 

 feature of these organs is the 

 absence of any gland -cells connected with them, such as are found 

 in the chemical sense-organs described on an earlier page. 



In one very important respect there is a marked difference in the 

 accounts of these organs that have been published. The organs were 

 first discovered long ago by Hicks ('57); but they have been more 

 carefully studied in recent years by several writers, who have been 

 able to make use of a greatly improved histological technic; among 

 these writers are Berlese (09 a), Vogel ('11), Hochreuter (12'), Lehr 

 ('14), and Mclndoo ('14). 



All of the writers mentioned above except the last named maintain 

 that the sense-cell ends in a structure, in the middle of the sense-dome, 

 which differs in appearance from both the membrane of the sense- 

 dome and the body of the sense-cell. This 

 structure varies in form in different sense- 

 domes; in some it is cyHndrical, and is 

 consequently described as a peg; in others, 

 it is greatly flattened so that it is semilunar 

 in form when seen in section. In Figure 

 175, ^. which represents a section made 

 transversely to the long axis of this part it 

 appears peglike ; but in Figure 175,0, which 

 represents a longitudinal view of it, it is 

 semilunar in form. 



According to Mclndoo (Fig. 176) no structure of this kind is 



Fig. 176 — Olfactory pore 

 of Mclndoo (From 

 Mclndoo) 



