ORGANS OF SMELL 



273 



religtosa the pits were not detected, but 011 each joint, except the 

 eighth basal, there a,re about 200 small, hollow, curved teeth with a 

 fine opening in front. 



In the Xeuroptera (Chrysopa) there occur on the antennae, besides 

 numerous very long tactile bristles, small pale, transparent teeth. 

 No pits could be detected. 



In the Hemiptera (two species of Pyrrhocoris only were examined) 

 only two kinds of tactile bristles occurred, but Hauser detected no 

 pits, though Lespes states that they are present. 



Of the Diptera, Hauser examined more than GO species. The 

 pits in the Diptera brachycera (Muscidae, etc.) are unexceptionally 

 confined to the third antennal joint. Their number varies extraor- 

 dinarily in the different species. Helophilus Jforens has on each 

 antennal disk only a single pit, while 

 Echinomyia grossa possesses 200 of them. 

 In flies of certain families the pits are 

 compound, and contain 10, 20, and often 

 100 olfactory hairs, partly arising from 

 the coalescence of several pits. Such pits 

 are usually divided by lateral walls into 

 several chambers, whose connection is only 

 indicated by their common outlet. Simple 

 olfactory pits with a single olfactory style 

 were observed only in the Tabanidae, 

 Asilidae, Bombylidae, Leptidae, Dolichopidae, 

 Stratiomyidae, and Tipulidte. In the last 



the Compound forms do not OCCUr at all, FIG. 272. Longitudinal section 



of apex of palpus ot Pieris orus- 



but in the other families mentioned also *^'<-' *<?*. scales; ch, cuticuia: 



. . fn/ji, hypodermis; , nerve; , 



OCClir Compound pits, receiving from two sense-cells;**, sense-hairs. After 



Vom Kath, from Sharp. 



to ten nerve-terminations. 



The antennal pits of flies are always sac-like invaginations of the 

 external chitinous integument, of manifold shapes, opening exter- 

 nally and never closed by a membrane. The pits differ but slightly 

 in the different species, and that of Cyrtonenra stabulans (Fig. 273) 

 is described at length as typical of those of brachycerous flies in 

 general. 



The olfactory pits of the Tipulidae seem to have a somewhat 

 different structure, since the external passage is closed. It is cir- 

 cular, surrounded with a slight chitinous wall, and not covered 

 with bristles. Such pits in their external appearance are like 



n 



organ discovered by him on the end of the palpus of butterflies, in which a number of 

 hair-like rods (sh) are seated on branches of a common nerve (n, Fig. 272). 

 T 



