146 DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 
altered in the antennae ; but in the palpi they retain their features perfectly, as is shown 
at PL XIX. fig. M, 4. There is also another peculiarity in these antennae, that on each 
side is an oval space where the integument is very thin, and covered closely by a great 
number of very delicate hairs, and to this part a large portion of the palpal nerve can be 
traced. The larva of Dyticus margmalis presents extremities somewhat on the same plan 
(PL XIX. fig. N, 1, 2, 3) : on the apex of each of the three palpi are short conical hairs ; 
on the external maxillary there are only two, on the internal maxillary three, and on the 
labial palpi four. 
Many of the Orthoptera possess palpi, the apical segment of which is dilated, and 
is described by many to be terminated by a white, transparent, distended bladder, upon 
which the main nerve of the maxilla and tongue spreads, and distributes itself upon its 
superior surface, with the finest branches (Burmeister) . This bladder, however, instead of 
being smooth, is furnished all over with numerous hairs, which differ from the others on the 
palpi in being much smaller and more delicately formed and evenly distributed, as is repre- 
sented in the palpi of Tetrix (PL XIX. fig. 0, 1). An enlarged view of the hair is shown at 
fig. 2. The length of each hair is about two inch, the diameter at the base is ^ inch, 
while the diameter of the elevation from which it grows is ttoo inch. If the hair is 
compared with the smaller palpal hairs of Dyticus marginalis (PL XIX. fig. E, 2), a strong 
resemblance will be seen. This condition exists in all the Orthoptera I have examined, 
the hairs being as strong and well-marked as in Tetrix ; they are well shown in Gryllus, 
Aclieta, Dlatta, &c. 
A common form of the termination of palpi is shown in the Hive-Bee (PL XVIII. 
fig. B, 4), and in the Megachile and Nomada (PL XIX. fig. A, 2, and fig. B), in the 
Scorpion-fly (Fanorpa communis) (PL XIX. fig. P, 1, 2, 3), in Formica (PL XIX. fig. Q, 1)- 
In these the hairs are shorter than the general form of hairs, — still not so much so as 
those above described, but they are placed on the most prominent points of the apex, 
evidently for the purpose of touch. 
Some palpi have no rounded bladder-like membrane, but simply a pointed extremity ; 
this, I believe, exists chiefly in the larval state. I have figured the internal maxillary 
palpi of the larva of Colymbetes striatus at PL XIX. fig. B, 1 a. On the apex of the 
maxillary and labial palpi are a number of small papillae, as at fig. B, 2 & 3. The 
nerve can also be seen running up to these papillae (fig. B, 3 a) ; the diameter of each 
papilla is 10 , 000 inch. These papillae are so exposed and unprotected by any hairs that 
doubtless they are used as instruments of touch. Compared with those of the perfect 
insect, they are very different, the latter being very similar to those of Dyticus margmalis 
at PL XIX. fig. E. 
A very peculiar form of palpus is that of Forficula auricularis, in which there is no 
such delicate membrane ; but the centre of the apex rises up in a cylindrical form, as 
in PL XIX. fig. S. The apex of this cylinder is closed across by a very thin membrane, 
the centre of which again is elevated, so as to form a large papilla ; around this latter 
there can be discerned very delicate hairs. To it also the nerve passes, as at fig. S, 2. Both 
palpi are alike. 
In those palpi with a delicate bladder-like termination, the membrane 
imm 
