Dr. Hagen writes to me—‘It is only in certain species that life is so short. The female Palingenia does not live long enough to complete the last moult of the sub-imago. I believe that a female imago has never been seen. The male imago, often half in its sub-imago skin, fertilizes the female sub-imago and immediately the contents of both ovaries are extruded, and the insect dies. It is quite possible that the eggs pass out by rupturing the abdominal segments.’
Libellula. All dragon-flies live in the imago condition for some weeks; at first they are not capable of reproduction, but after a few days they pair.
Lepisma saccharina. An individual lived for two years in a pill-box, without any food except perhaps a little Lycopodium dust[[9]].
II. Neuroptera.
Phryganids ‘live in the imago stage for at least a week and probably longer, apparently without taking food’ (letter from Dr. Hagen).
According to the latest researches Phrygane grandis[[10]] never contains food in its alimentary canal, but only air, although it contains the latter in such quantities that the anterior end of the chylific ventricle is dilated by it.
III. Strepsiptera.
The larva requires for its development a rather shorter time than that which is necessary for the grub of the bee into the body of which it has bored. The pupa stage lasts eight to ten days. The male, which flies about in a most impetuous manner, lives only two to three hours, while the female lives for some days. Possibly the pairing does not take place until the female is two to three days old. The viviparous female seems to produce young only once in a lifetime, and then dies: it is at present uncertain whether she also produces young parthenogenetically (cf. Siebold, ‘Ueber Paedogenesis der Strepsipteren,’ Zeitschr. f. Wissensch. Zool., Band. XX, 1870).
IV. Hemiptera.
Aphis. Bonnet (‘Observations sur les Pucerons,’ Paris, 1745) had a parthenogenetic female of Aphis euonymi in his possession for thirty-one days, from its birth, during which time it brought forth ninety-five larvae. Gleichen kept a parthenogenetic female of Aphis mali fifteen to twenty-three days.