ALTERNATION OF GENERATIONS. 51 



the Entomological Society of Philadelphia). Parthenogenesis, 

 or agamic reproduction, is, then, the result of a budding pro- 

 cess, or cell-growth. This process is a common mode among 

 the Radiates, the low Worms, and the Crustaceans. Metamor- 

 phosis is simply a series of marked stages, or periods, of 

 growth ; and hence growth, metamorphosis, and agamic re- 

 production are morphologically identical. All animals, there- 

 fore, as well as plants, grow by the multiplication of cells. 



After hearing the surprising revelations of Bonnet, Reaumur, 

 Owen, Burnett, and Huxley on the asexual mode of generation 

 in the Aphis, we are called to notice still a new phase of repro- 

 duction. None of the observers just mentioned were accus- 

 tomed to consider the virgin aphis as immature, but rather as 

 a wingless adult Plant-louse. But Nicolas Wagner, Professor 

 of Zoology at Kasan,* supported by able vouchers for the 

 truth of his assertions, both in Russia and in Germany, who 

 have repeated and thoroughly tested his observations, has 

 observed an asexual reproduction in the larva of a Cecidomy- 

 ian fly, Miastor metraloas (Fig. 297), and Meinert has observed 

 it in this species and the Oligarces paradoxus Meinert. 



Says Dr. R. Leuckart, whose article f we have drawn largely 

 upon in the present account, "This reproduction was said to 

 commence in autumn, to continue through the winter and 

 spring, giving origin, during the whole of this period, to a 

 series of successive generations of larvae, until, finally, in June, 

 the last of them were developed into perfect and sexually 

 mature animals. The flies, then, as usual, after copulation, 

 lay eggs, and thus recommence the developmental cycle just 

 described." 



Professor Leuckart has observed these facts anew in the 

 larvae of a species of dipterous gall-fly, and which he believes 

 distinct from the Russian species, found under the bark of a 

 half dead apple-tree that was attacked by fungi. The young 

 are developed within the body of the larva-like parent from a 



*K. E. Von Baer, "Report on a New Asexual Mode of Reproduction observed 

 by Professor Wagner in Kasan." Bull. Acad. St. Petersburg, 1863, pt. vi, p. 239. 

 Also, Wagner in the Journal of the University of Kasan, 1861. 



f On the Asexual Reproduction of Cecidomyia Larvae. Annals and Magazine 

 of Natural History, March, 1866. Translated from Zeitschrift f ttr Wissenschaftliche 

 Zoologies Bd. xiv. 



