448 EXTERNAL ANATOMY OF INSECTS. 



is, that the maxillary shall be longer than the labial ; but 

 the reverse often takes place. In many bees the maxil- 

 lary consist only of a single joint, and are very short ; 

 while the labial consist of four, and are very long a : and 

 in some insects (as in Pogonophorus Latr.) the four palpi 

 are of equal length b . The antennae are most commonly 

 longer than the palpi ; but in several aquatic beetles, as 

 Elophorus, Hydrophilus, &c, whose antennae in the wa- 

 ter are not in use, the organs we are considering are the 

 longest. — As to the number of their articulations, it va- 

 ries from one to six ; which number they are not known 

 to exceed. In each of the Orders a kind of law seems 

 to have been observed as to the number of joints both 

 in the maxillary and labial palpi, but which admits of 

 several exceptions. Thus in the Coleoptera, the natural 

 number may be set at four joints for the maxillary, and 

 three for the labial palpi : yet sometimes, as in Stenus, 

 Notoxus, &c, the former have only three joints, and the 

 latter, as in Stenus and Tillus, only two. In the Ortho- 

 ptera the law enjoins^r^ for the maxillary, and three for 

 the labial; and to this I have hitherto observed no ex- 

 ception. In the Hymenoptera, the rule is six and four, 

 but with considerable exceptions, especially as to the 

 maxillary palpi, which vary from six joints to a single 

 one : thus in the hive-bee and the humble-bee, the la- 

 bials, including the two flat joints or elevators, have four 

 joints, while the maxillaries are not jointed at all c . In 

 Chrysis, in which the latter consist of Jive, the former are 

 reduced to three. The Libellulina may almost be re- 



a Mon. Ap. Angl. i. t. ix. 2. c. 2. /3./. 2. d. g. 4. t. xii. neut.f. 6. d. 

 t. xiii./. 3. b. *> Clairv. Ent. Helv. ii. t. xxiii./. 1. 



c Plate VII. Fig. 3. b". h". 



