54 



ANTENNA OF ICHNEUMON. 



there are larger orifices leading into more complex de- 

 pressions, apparently arising from the confluence of a 

 number of the simple sacs. At the base of these large sacs 

 are a number of papillae, or small hairs. In the dragon- 

 fly, each segment of the antenna contains a large con- 

 voluted sac. The sacs, in fact, vary much in number, 

 size, and form, but Hicks considered that "they all 

 possess the same elements, and are formed on the same 

 principle." In many cases he traced a nerve to the 

 base of the pits. He considered 

 that they were generally, if not 

 always, closed in by a deli- 

 cate membrane, which, indeed, 

 sometimes projected in a 

 hemispherical, conical, or even 

 hair-like form. 



The minute structure of the 

 pits was further studied by 

 Leydig in 1860. He describes 

 them as parts of the integument 

 in which the chitine is very 

 thin, and more or less depressed, 

 centre. This hair may be even 



Fig. 41.— One segment of the an- 

 tenna of an Ichneumon (after 

 Hicks). 



with a hair in the 

 reduced to a mere ring. 



Hicks also called attention to a remarkable speciality 

 in the antennae of the Ichneumons, the true nature of 

 which he did not, however, correctly ascertain. He 

 describes the appearance presented as that of a great 

 number of narrow inverted canoes, with a keel-like 

 ridge, and each inverted over an oval perforation. He 

 regarded these as consisting of a thin transparent 

 membrane. Subsequent observations, however, have 

 shown that each supposed canoe-shaped membrane is, 



