140 DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 



to draw attention to another somewliat similar group of organs observed about the joint of 

 the trochanter and femur, chiefly on the former, and which I have found in all the insects 

 I have examined. 



The organs in question consist, as in the structures above described, of a thin delicate 

 membrane, probably the cuticle, stretching over, and closing in from the air, a tubular 

 aperture in the chitine-layer of the part. This apertmx may be circular or oval, the tube 

 varying in length according to the thickness of the integument, curved as in the Hornet, 

 or forming a globular cavity as in Silpha. The delicate membrane which covers over this 

 aperture is generally level, sometimes having a ridge or a minute papilla in its centre, as 

 in Meloe (PI. XVIII. fig. G). 



In some rare instances, as in Formica rufa (PI. XVIII. fig. M), I have found that a few 

 occur about the next joint (the tarso-femoral). 



The following are those which I have selected to exemplify these structures : — 



They are remarkably well shown in the genus Rippobosca. Fig. C, 1, represents the 

 trochanter-femoral joint of S. Mmmdinis. The organs are found on both sides of the 

 limb, and occur in groups of one or two rows of vesicles, each of which has a diameter of 

 3^5-0 inch, the rows being either straight or curved. 



Fig. 0, 2, shows those of S. Ovis ; they are rather more numerous than in H. Hirmi- 

 dinis, and of the same diameter. 



Those of H. equina are similar. 



Those of Mtf^sca domestica are represented at fig. D. In all the Diptera I have exa- 

 mined they are aUke; they are concentrated into a group of about ten to twelve on 

 the femoral portion of the joint. The diameter of each is 3^00 iiich. 



In Pulex these organs can be seen, of a smaU size, about three in number, on the concave 

 side of the trochanter. They are best shown in the SwaUow-Plea. 



In Silpha (PI. XVIII. fig. E) they are weU marked, being about eight on one side of 

 the trochanter and six on the other, the centre of the tube being of much greater diameter 

 than either the covering-in membrane or the internal opening, thus being of a globose 

 form. The diameter of the covering-in membrane of the largest is yriVo inch. 



In the female of Lampijris nocUluca (Glow-worm) (PL XVIII. fig. F) they are found 

 in a row of six to eight, extending transversely across the trochanter on each side. The 

 branches of the nerve proceeding to them can be i)lainly seen (fig. F, 1 c). 



In Sleloe I have found these organs on the femur, close to the trochanter; they 

 are about twenty in number; the covering-in membrane has a central prominence 

 (PI. XVIII. fig. G, 2 ^», 3 6), on which the branch of the nerve (fig. G, 1 «, 3 a) ends, after 

 passing up the tube in the integument. The diameter of this covering-in membrane is 

 about ^tVo inch ; that of the papilla is —5^00 i^^ch, whilst that of the nerve is still smaller. 



In Forficula auricidaris (PI. XVIII. fig. H) they are found on each side of the tro- 

 chanter, near the joint, on one side rather scattered and large, and on the other in 

 a group of about six or seven. They are oval in form, and rather prolonged at one end. 

 The diameter of the longest is jtoo inch. 



These structures are found in the Grasshoppers {Tetrix) on both trochanter and femur, 

 as shown in PI. XVIII. fig. I, 3 ; they are oval, and in the common Grasshopper mea- 



