DB. J. B. HICKS ON A NEW OBGAN IN INSECTS. 137 



to the middle leg; and the fourth (the largest of all) passes 

 straight into the halteres ; the fifth set supplying the posterior 

 legs. I have drawn the nerves of the Drone (Plate Y. fig. 1) and 

 Blow-fly (fig. 2). 



In the Lepidoptera there are two thoracic ganglia. The first 

 (the smaller) supplies the anterior legs. The second gives off the 

 first pair to the anterior wings, the second pair to the middle 

 legs, the third pair to the second wings, and the fourth to the 

 posterior legs. 



In the Lucanus Cervus (Coleoptera) we find three thoracic 

 ganglia : the anterior supplies the first pair of legs ; the second 

 gives a pair to the elytra and a pair to the middle legs ; while the 

 third ganglion supplies a pair to the second wings and the poste- 

 rior legs. 



In the Orthoptera, in the Locust for example, the arrangement 

 is similar as to the origin of the nerves. 



In the Hymenoptera the arrangement is as in the Lepidoptera. 



In the Neuroptera (Dragon-fly) there are three thoracic ganglia, 

 the nerves passing off in the same manner as in the Lucanus 

 Cervus. 



In the Hemiptera the thoracic ganglia are fused into one, as in 

 the Fly. But the nerve to the anterior wing is twice the size of 

 that to the posterior. 



From the above statement, it will be seen that we find in all 

 insects — 



1st, A pair of nerves going to and entering the base of each of 

 the wings ; and in the Diptera, of the halteres also. 



2nd, The nerves supplying the posterior wings or halteres are 

 generally the larger. 



As there are no muscles in either the wings or halteres, these 

 nerves must be sensatory. 



I shall now describe the curious organs to which they proceed. 



And first as regards the halteres. Situated on the pleura, and 

 closely adjoining a large spiracle, we find the joint very free, so 

 that these organs can be moved with such rapidity as to render 

 them invisible when in motion ; and they are beautifully protected 

 in the Fly by the scales, which in Rhingia rostrata form a very 

 beautiful object. 



The halteres consist of a base, shaft, and head; the relative 

 proportion of each varying in different insects. On each side of 

 the base is a ridge, and on these ridges are situated two similar 

 structures. In the Bhingia rostrata (Plate V. fig. 3), for instance, 



LINN. PBOC. — ZOOLOGY. 10 



