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



altered in tlie antennas ; 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 hy 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 hau's ; 

 on the external maxillary there are only two, on the internal maxiUary 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 difiPer from the others on the 

 palpi in being much smaller and more delicately formed and evenly distriljuted, 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 yooo i^ch, the diameter at the base is -g^oo iiich, 

 while the diameter of the elevation from which it grows is 2^00 iiich. If the hair is 

 compared with the smaller palpal hairs of Dyticns margmalis (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 Tetrkv ; they are well shown in Grylltis, 

 Aclieta, Blatta, &c. 



A common form of the termination of palpi is shown in the Hive-Bee (PL XVIII. 

 fig. R, 4), and in the IlegacUle and Nomacla (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 Colymhetes striatns at PL XIX. fig. R, 1 a. On the apex of the 

 maxillary and labial palpi are a number of small papillae, as at fig. R, 2 & 3. The 

 nerve can also be seen running up to these papiUse (fig. R, 3 a) ; the diameter of each 

 papilla is yoTttoo i^ch. 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 marginalis 

 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 commences 



