1G8 METAMORPHOSES OF MAN 



we descend in the scale of beings, as though Nature 

 were compelled by the very simplicity of the organisms 

 to multiply the means necessary to ensure repro- 

 duction. 



In the outset we may state that no vertebrate 

 animal is reproduced by geneagenesis, and that this 

 form of reproduction is very rare among highly 

 organized invertebrates. In the insect class, where 

 the species number a hundred thousand, very few 

 examples beyond those of aphides are known.* 

 About the most remarkable, is that of one of the 

 hymenopterous family, Pteromalidse (Ophionurus) ,t 

 which was discovered by Dr. Philippi. This insect, 

 like many of its kindred, deposits its ova in the egg 



* I agree with Owen, Steenstrup, Van Beneden, Carus, &c., 

 in considering the agamic reproduction of aphis to be due to a 

 process of internal budding. It has been proved by the researches 

 of these naturalists that the reproductive bodies which are developed 

 during summer in the wingless aphides are simple deciduous buds. 

 Leydig, a German naturalist well known through his important 

 •writings, believed he had satisfied himself that these bodies are 

 genuine eggs which are hatched within the mother's oviduct. If 

 this view were correct, the aphides would be ovo-viviparous, and it 

 would be no longer a question of geneagenesis but rather of par- 

 thenogenesis, which we shall treat of hereafter. But this opinion, 

 which seemed to support Heiden's observations, to which we 

 alluded some few pages back, was refuted by the new and very 

 accurate researches of Leuckart, Lubbock, and especially of Huxley, 

 which will be discussed further on. 



t " Annales des Sciences naturelles," 1851. The order Hymen- 

 optera includes all insects akin to the bee and which are provided 

 with four membranous wings, and the PteromalidaB constitute one 

 family of this order. Philippi's observations were at first con- 

 tested, but he afterwards confirmed them by a series of new re- 

 searches, in his " Troisieme Memoire sur l'Histoire genesique des. 

 Trematodes." — Memoires de l'Academie des Sciences de Turin^ 

 1857. 



