254 Transactions of the Society. 



although they have supphed the greatest number and variety of 

 examples. Among these it really would seem as if all the ortho- 

 pterous insects have them, and most of the Neuroptera. Some are 

 very minute, even when the owner is of large size ; others greatly 

 elongated, as in Lucina opilioides, where the organ is over an inch 

 long. Curious instances may be found in Thuxalis, in Heterodes ; 

 also in an Indian Grasshopper (possibly anonymous), which has the 

 organ twisted, and tipped with a hard serrated hook. 



As regards the function of pygidia, it might appear, at first 

 sight, that the new examples being mostly of large size, there 

 would be little difficulty in investigating and determining a matter 

 which, in the case of Pulex, has vainly taxed the skill, patience, and 

 acumen of many excellent observers ; and probably if the subject 

 were taken up again by biologists well versed in the anatomy and 

 physiology of insects, satisfactory results might accrue ; but as a 

 matter of fact, the inquiry is by no means an easy one, and after 

 considerable study of fine and various specimens, I, for a long time, 

 only arrived at a conclusion — an old one, it would seem, of the late 

 Mr. llichard Beck — that pygidia are collections of tactile hairs 

 forming posterior feelers ; but quite lately, almost by an accident, 

 I was enabled to see that, while they may be this, they certainly 

 are something, and very much, more. 



I had a pygidium of a Cricket under a low power,and was surprised 

 to see a strong, waving motion in the hairs ; this, at first, was attri- 

 buted to action imparted at the will of the insect, although it was 

 at the time stupefied and quieted with chloroform ; but the same sort 

 of movement occurred when the creature was quite dead, and when 

 only a thin section of the organ was under the Microscope. It was 

 found that the hairs are so light and so delicately attached, that the 

 ordinary breathing of the observer, at fully ten inches distance, set 

 them in motion ; and a slight movement of the hand a foot or more 

 away caused a visible disturbance, which is not a mere vibration, 

 but a rocking of the motile hair in its socket, and of the disk by 

 which it is attached. In repeating this exj)eriment, it is necessary 

 to examine the part within a short time of the death of the insect, 

 and before the rigor mortis has set in ; otherwise the little disk at 

 the base of the hair (sometimes there is a rounded end, but never 

 a root) will become more or less firmly fastened to the white 

 (nervous ?) matter in which it seems set, and the hair will be found 

 comparatively insensitive. 



It will be seen that as mere tactile hairs they are far too 

 delicate ; moreover, examples may be found in some species of 

 Lace-wing, and notably in the Flea of the Pigeon, where by being 

 surrounded by coarse true hairs, or placed under stout curved 

 spines, they are partly or wholly protected from contact with 

 external bodies. I am led to believe pygidia to be collections of 



