EXTERNAL ANATOMY OF INSECTS. 483 



discover a minute membranous protuberance under eacli 

 angle ot the nose. Something similar may be observed 

 in some species of Asilus L. In the Ortkoptera, espe- 

 cially in Blatta, Phasma, and some Locusta?, two roundish 

 or square pieces, close to each other on the lower part 

 of the nose, represent the nostrils a . — With regard to 

 substance, in the chafer- tribes, at least those that feed 

 on leaves or living vegetable matter, as the Melolon- 

 thidce, Anoplognatludce, and in many other insects, the 

 rhinarium is of the same substance with the rest of the 

 head; but in Macropus Thunb., Staphylinus, Necrophorus, 

 &c, it consists of membrane. 



ii. Postnasus b . — This is a part that appears to have 

 been confounded by Entomologists with the front of in- 

 sects; in general, indeed, it may be regarded as included 

 in the nose, and does not require separate notice : but 

 there are many cases in which it is distinctly marked out 

 and set by itself, and in which it forms a useful diagno- 

 stic of genera or subgenera. There is a very splendid 

 and beautiful Chinese beetle, to be seen in most collec- 

 tions of foreign insects (Sagra purpurea), in which this 

 part forms a striking feature, and helps to distinguish the 

 genus from its near neighbour Donacia. If you examine 

 its face, you will discover a triangular piece, below the 

 antennas and above the nasus, separated from the latter 

 and from the front by a deeply-impressed line : this is the 

 postnasus or after-nose. Again : if you examine any spe- 

 cimens of a Hymenopterous genus called by Fabricius 

 Prosojns (Hylceus Latr.), remarkable for its scent of 

 baum, you will find a similar triangle marked out in a 



1 Plate VI. Fig. 4. g'. b Plates VI. VII, b. 



2 i 2 



