OF SUCTION IN LYGUS PABULINUS. 691 
The Maxillary Palps. 
The presence of maxillary palps is one of the distinguishing 
features of the first maxille of the biting insects, but they 
have completely disappeared in the Rhynchota. The maxille 
become elongated in these insects, and work inside plant or 
animal tissues. Sensory apparatus in the form of palps is 
superfluous. 
Maxillary palps had been described long ago by Ratzeburg 
(1827-34) in certain species. Hach palp was found to be three- 
jointed. Burmeister (1835) had, however, found that they were 
not palps but horny tubercles marking the attachment of the 
maxillary muscles. 
Heymons has, as far as possible, elucidated the question of the 
maxillary palps. According to Smith, the maxillary sclerite and 
the palps fused together to form one structure. Heymons, 
however, holds another view. The maxillary palp is distinct 
from the sclerite, and the maxillary plate has a process (processus 
maxillaris) which he interprets to be the remains of a maxillary 
palp. In some species of Tingide there are certain processes— 
which were taken to represent the labial palps—but which are 
now regarded as the maxillary palps. 
Rudimentary palps are present in some Hydrocoridee—in 
Nepa they are onion-shaped—but in Gymnocerata they are 
identified with the Bucculz (?). 
Mandibles, or external Stechborsten. 
These were recognised as such long ago, though Kraepelin (25) 
had mistaken them for the maxille, and had therefore made 
them the sucking organs. The views of Mecznikow have been 
given above. Prof. Smith, while working on the nymph of 
Cicada, described a mandibular sclerite corresponding to that of 
the maxilla, and a mandibular stylet also corresponding to the 
maxillary. Heymons, too, has described the mandibular sclerite 
(lamina mandibularis) and stylet in Cicada. The mandibular 
sclerite is very well marked in the Homoptera, but in the 
Heteroptera it is not present at all, or is rudimentary. These 
structures are distinct in the later stages, though they have been 
derived from the same structure in the embryo; the connection 
between them is lost. The protractors of the mandibular stylets 
are not attached to the mandibles but to their levers at one 
end and, at the other, to the mandibular sclerite. 
This interpretation of Heymons has been recently called in 
question by Muir and Kershaw (22, 23, 24). The so-called 
mandibular plates are not derived, according to them, from 
the mandibles, and therefore have no relation whatever to 
them. They are mandibular folds or sulci. 
The most recent view therefore is :—(i.) The mandibles of the 
biting insects are represented by the external stylets. (i1.) The 
mandibles are not divided into two parts, one corresponding to the 
