Aphididae of Formosa. — 3. 3 



a fifth moult suLsu(iiR:ut to tliu birth of young; and it lias hci.'ii stated that a fifth 

 moult has likewise been noticed exceptionally in 3Iacrofiiphicin jrisi Kalt. Mouzeu 

 observed that a moult took place after the birth of young in Eriosoma lanigera 

 Hausm. The moulting after sexual maturity observed in some Aphididae is also 

 known in C'oUembola, but not in any other order of insects. 



Moreover it is very remarkable that, unlike all other groups of insects, Aphi- 

 didae, as ^\•ell as Collembola, are not provided with malpighian vessels. This is in 

 support of the theory that ccdysis perhaps has an excretory importance besides 

 being a provision for growth. 



Ewing obtained paedogenetic nymphs, as he designated tliem, of Uhopalosiphum. 

 avenae Fab., but as pointed out by Baker, these proved to be intermediates, adults 

 Ixitween the winged and wingless condition. 



Paedngenesis has not been found in Aphididae. The number of moults is few 

 in the sexes of PemphUjus, Tetraneura , Eriosoma and others, as well as in the 

 males of Stomapjlvis. These sexual forms are always apterous, with the rostrum 

 rudimentary. 



I have found that the wingless forms of the genera Oregma and ylste.'jo/tterijx 

 moult only three times, while their winged forms moult four times as is usual in the 

 family. The apterous forms of Ldchnus tlmjafoUae Theob. likewise seem to have 

 three nymphal instars. Pergande records three moults for the apterous forms and 

 four moults for the winged forms in HorvuipMs hamameUdis Fitch and Hamavie- 

 listes spinosus Shimer. 



According to Fuller, the apterous workers and soldiers of a termite comm- 

 unity pass through fewer stages of growth than do their corresponding winged 

 imagoes. Certain apterous species of Gerridae and Veliidae have heen recorded as 

 having three or four nymphal instars, although five instars is the common number 

 for Heteropterous insects. In the author's opinion these facts indicate that the 

 apterous forms of paurometabolous insects show a tendency to moult fewer times 

 than do the winged forms. This is perhaps duo to the simplicity of structure of the 

 body in the apterous forms. 



Morphology of the nymphs, with 

 special reference to their metamorphosis. 

 As is well known, the postembryonic development of Aphididae is pauronn!- 

 tiibolous and, as in many other groups of paurometabolous insects, the structural 



