ia 
EXTERNAL ANATOMY OF INSECTS. 447 
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’: 
and in some insects (as in Leistus) the four palpi are 
of equal length>. The antennz are most commonly 
longer than the palpi; but in several aquatic beetles, 
as Elophorus, Hydrophilus, &c., whose antenne in the 
water are not in use, the organs we are considering are 
the longest.—As to the nwmber of their articulations, it 
varies 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 jive for the maxillary, and three for 
the Jabial ; and to this I have hitherto observed no ex- 
ception. In the Hymenoptera, the rule is siz and four, 
but with considerable exceptions, especially as to the 
maxillary palpi, which vary from szz 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*. In 
Chrysis, in which the latter consist of five, the former are 
* Mon. Ap. Angl. i. t. ix. 2. c.2. 8. f.2.d. g. 4. t. xii. neut. f. 6. 
d, t, xiii. f. 3. b. ’ Clairy, Ent, Helv. ii. ¢. xxiii. f. 1, 
* Prats VIE. Fie: 3. b"h”". 
