STEUCTUUE AND BIOLOGY OF SCHIZONEURA LANIGERA. 677 
Mecznikow (1866, p. 462) states tliat during the develop- 
ment of Aphididae, the structure in the early embryonic stages 
corresponding with rudimentary mandibles and maxillae dis- 
appear, and that the retort-shaped organs found in more 
advanced embryos become elongated at the neck end and 
produce the “ Russelstilette,” and Mayer (1875, p. 335), in 
describing the origin of the “ Stechborsten” in Pvrrochoris 
apterus, states that the retort-shaped organs observed 
throughout the development of this insect, are to be considered 
as the “ Bi'idungstatten ” of those structiu’es. Witlaczil (1882, 
p. 415) is of the opinion, that the embryonic “ Anlagen ” of 
the mandibles and tnaxillae do not disappear, but sink into the 
head, and give rise to the retort-shaped organs. 
1 propose to discuss the question as to the structure of these 
organs and their relation to the mandibles and maxillae in 
greater detail wlieti dealing with the anatomy of the larva,. 
4’ he Salivary Gr lands. — 'Ihie salivary glands are whitish 
glandular bodies, situated in the prothorax and posterior 
region of the head. 'I'hey consist of two pairs^ of glands, 
which lie above the thoracic ganglion, one pair on each side 
of the oesophagus. Kacli pair comprises a large posterior 
gland and a smaller anterior gland. 
4'he posterior salivary gland (.s. p.) is large, oval in shape, 
and lies obliquely in the ])rothoiax. 
'I’he anterior salivary gland (.s', a.) is small, spherical in 
outline, and situated close to the anterior end of the posterior 
gland. 
.‘V narrow duct leads from the anterior end of each 
posterior gland, near to which it receives a small duct from 
the anterior gland. 'I’he salivary duct from each side passes 
' In some Aphids three glandular bodies have been described, as in 
Phylloxera vastatrix (Krass, 1893); also in Aphis ribis (Fldgel, 
1905). In these cases, as Mordwilko (1895) points out, the large postei'ior 
gland described above, may be bi-lobed. The small anterior gland, on 
account of its small size, was overlooked by some of the earlier workers. 
Mark (1877) has figured the salivary glands of S . u Imi, which correspond 
closely to those in S. lanigera. 
