OF SUCTION IN LYGUS PABULINUS. 689 
segments of the galea. <All that remained of the labium was the 
mentum—a boat-shaped process lying between the stylets. This 
was an original view, confined to Smith alone. It was shown, 
the next year, to be erroneous by Marlatt (34), and, after a few 
years, by Meek (36), according to whom the boat-shaped process— 
the mentum of Smith—was the pharynx. 
Thus far no one has definitely demonstrated the presence or 
absence of the labial palps. All the recent writers are unani- 
mous in the view that the proboscis is formed by the fusion of 
the second maxille, which consist of the submentum, mentum, 
paraglosse, and ligule—the view held by Gerstfeldt long ago. 
But here unanimity ends, and different views prevail as to the 
existence of the labial palps. 
(i.) Leon holds that they are present in the adult forms. He 
deals with this question from the anatomical standpoint. 
(ii.) Heymons holds that the labial palps appear only in the 
embryonic stages, and disappear in the adult forms. He writes: 
“Wenn einigen Autoren auch gewisse Anhange an der Unter- 
lippe, also Palpi labiales angesprochen worden sind, so wird man 
sich diese Deutungen gegeniiber skeptisch verhalten miissen, da 
weder die Entwickelungsgeschichte, noch die vergleichende 
Anatomie zu Gunsten solecher Ausnahmen sprechen.” 
Maxille, or inner Borstenkiefer, or Stechborsten. 
Savigny long ago, and others who have followed him, have 
homologised the inner stylets of the Rhynchota with the first 
maxille of the biting insects. But they have not clearly shown 
what parts correspond to cardo, stipes, etc., and what becomes 
of the maxillary palps—which are conspicuously absent in the 
Hemiptera. 
Kraepelin (25) held that the grooved inner stylets were 
mandibles, which formed the tube for suction, while the maxille 
were on the outside of the mandibles. This view is not now 
accepted. 
Huxley (48) denied the homologies of the inner stylets with 
the first maxille of the other (biting) insects, because the former 
do not happen to possess the maxillary palps of the latter. 
Mecznikow (49) has also denied the homologies of the internal 
and the external stylets in the Homoptera. According to 
him the true maxille and mandibles appear in the embryonic 
stages only, but they degenerate and disappear later on. Both 
stylets of the adults are produced from the retort-shaped 
(‘‘retortenformigen”) organs situated in the head. They are 
therefore not homologous with the maxille and the mandibles of 
the biting insects. 
Witlaczil (50) has demonstrated, however, that the embryonic 
mandibles and maxille do not disappear at all, but persist in 
the adult stages, though there is a marked change in their 
position. In early stages they are situated on the outside, but 
later on they sink into the head and become entirely internal. 
