PARTHENOGENESIS IN THE ANIMAL KINGDOM. 241 



society iu February, 1805, it hardly seems to dilier from the geuus 

 lieteroiieza Winncrtz. Eeproductiou takes place by means of germs. 

 From seven to ten of these arise out of the accumulated i)lastic material 

 in the body of the " mother-larva," and develop to ''■ daughter-larvie." 

 The former is thereby gradually destroyed, and the progeny tears her 

 skin and passes out. After three or live days the same process of 

 germination begins iu the new larva, and this continues from August 

 to June, when all the larvtie of the last generation simultaneously pass 

 into the pupa state. After three or four days the perfect insect, a 

 small reddish-brown tly, emerges from the pupa. The correctness of 

 these observations was afterward verified by v. Bicr and v. Siebold, 

 and Professor Alexander ragenstecher, of Ileidelberg, observed the 

 same thing in another species and accurately described it.* 



Metagenesis, with mature individuals as nurses, is exemiilified among 

 the arthropods by the aphides. As early as the middle of the last cen- 

 tury, Charles Bonuet t had already communicated exact observations on 

 the peculiar and remarkable mode of reproduction of the aphides, (plant- 

 lice.) These well-known enemies of our gardens and green-houses cover 

 the leaves, shoots, and branches of certain plants in thick swarms, and 

 defy all our exertions to get rid of them by their extreme fecundity. 

 During the summer there is a series of nine or ten generations of fully- 

 formed but sexless animals, or nurses, which bring forth living young 

 without fecundation, and even without the presence of the male. Em- 

 bryos are formed immediately from germs, which do not show the struc- 

 ture of true ova. They separate from peculiar tubes (germinal tubes) 

 and develop in the body of the mother. In autumn the next to the tost 

 generation produces sexually-developed males and females, which really 

 cohabit. As in most insects, the male then perishes, while the female 

 lays eggs, which hibernate and produce a new race of nurses the following 

 spring. The anatomical examination of these animals, which was first 

 undertaken by v. Siebold, and afterwards confirmed by Leidig, shows 

 that the viviparous individuals are well developed, and resemble the 

 oviparous females of the last fall generation, but that they are sexless 

 nurses, becauses they lack the seed-bladder belonging to all female in- 

 sects, and are, therefore, incapable of receiving the male seed. 



All the phenomena of alternate generation were also called '■^ FarfJicno 

 f/niesis^' by the excellent English anatomist, Richard Owen, in 1S4!),| 

 and this name, although somewhat inappropriate, was generally received 

 oa account of its euphony. When, however, the surprising discoveries 

 of the last few decades put in question the theory that " every true egg 



* Zeitschrift fiir wissedsch.aftliclic Zoologie, xiv, p. 400. Further iuvestioatiou of 

 this subject is communicated by L(suckart, iu Troschel's Archiv., year XXXI, No. 3. 



+ Trait<5 d'Insectologie, tome I : Paris, 1845. 



t On Parthenogenesis ; a discourse introductory to the Hunt^riau Lectures on gen- 

 eration and development for 1849. Delivered at the Royal College of Surgeons of 

 England : London, 1349. 

 10 S 71 



