IN THE ANTENNÆ OF INSECTS. | 151 
The diameter of the simple sacs is about 3357 inch, that of the largest from sopọ to 
1300 inch; the length of the longest sac 445 inch. 
In the Grasshoppers (Tetrix) (Tab. XXX. fig. 11) I find a structure very similar to 
that of the simple sacs of Libellula, and formed in the same manner ; but there is a distinct 
papilla (of which there is some trace in Libellula) in the centre of the floor of the sac 
(probably where the nerve is connected with it), and from this papilla a small chain of 
minute bodies extends to the centre of the membrane which closes the aperture. This 
connexion is well seen ‘in profile (fig. 11, e 1), and, when viewed from above, the point of 
contact with the external membrane is seen in the centre, as is indicated in fig. 11, B. 
The diameter of those represented in fig. 15, is about 5555 inch. There are about 
twenty-two joints in this antenna, the lower of which possess about twelve sacs; the 
number inereases towards the apex, till about from the fourteenth to the last there 
are 100 on each, so that we may estimate the total number on each antenna to be at 
least 1000. 
In Gryllus, Gryllotalpa, and Blatta, I have found these structures in each joint of 
the filiform antenna, generally from two to four in number, and commonly occupying 
the same position and aspect of the joint. I have drawn those of Gryllus domesticus at 
Tab. XXX. fig. 12. 
In the Coleoptera, so far as I have examined, similar organs are to be met with. 
In the attenuated antenna of the Longicorns, they are placed near the upper end of 
each joint, where they form groups of eight to ten, one group on each side. 
In Silpha clavicornis they are scattered mostly on one side of the thickened joints, the 
membrane by which the aperture is closed projecting hemispherically. 
In Melolonthå vulgaris the whole surface of the lamella is thickly covered by organs. 
which are apparently of similar structure; these are figured in Tab. XXX. fig. 12. 
` They consist of an irregularly-round cup-like depression, the centre of which rises up 
nearly to the external surface of the antenna. From this projection a tube runs inwards 
quite through the internal layer of the wall of the antenna, while the external end 
- which forms the central projection is closed by a delicate membrane. s i 
. . The diameter of the cup is about 5545, while that of the central projection is 3757 inch. 
The external layer of the cuticle is marked by hexagonal lines so disposed that each of 
the cups occupies one of the areas considerably enlarged. Tan 
The nerve entering the antenna is large, and at the base of each lamella sends into it a 
branch, which dividing into four or five smaller branches, spreads out over the whole 
internal surface. 
The number of these organs on each antenna 1s as > y Å 
each lamella is about 2 inch by 7 inch; each square of 4, inch has on each side 45 o 
these structures; the square would therefore hold 2025. As there are four of these 
areas in the entire side of the lamella, the number would be 8180. The sum for both 
sides will be 16,360, and as there are seven lamellæ on each antenna, the total number 
of these organs on the whole antenna will be 114,520. A deduction of 2000 or 3000 
may be made for irregularities, difference of size, &c. ; still, making the most liberal 
. deduction, we may say there are at least 100,000 on each antenna. 
follows. - The area of one side of 
