OF MAN AND THE LOWER ANIMALS. 39 
female parent at once, reproducing its species in the normal 
manner without intercourse with another individual?” No 
satisfactory answer could be obtained to this query; reason 
seemed to reply in the ailirmative, but all experiment and 
observation failed to confirm such a conclusion. The re- 
searches of Bonnet, the pupil and co-operator of the illustri- 
ous Réaumur, brought about a new phase in the history of 
this subject. It had been suspected already that among the 
plant lice (Aphides), each individual possessed the two sexual 
attributes. ‘To ascertain the truth of this suspicion, Bonnet 
isolated one of these imsects almost immediately after 
birth, and proceeded to watch it most attentively. In 
eleven days the virgin aphis produced a young one, 
and in twenty-one days, no less than ninety-five. More- 
over, Bonnet found that this power of reproduction, sine 
coitu, resided also in the individuals already obtained, ex- 
tending in some cases to the tenth generation. He found, 
however, that in the fall of the year sexual intercourse did 
occur, and eggs were deposited as in other insects, the 
irregular cases of virginal reproduction taking place only in 
summer. It would have been easy to account for the latter 
phenomena by the theory of androgynism, had it not been 
accompanied by the normal process and the existence of dis- 
tinct males and females. Various explanations were hazarded, 
the most in vogue, and at the same time that which was 
most accredited until of late years, being that the force of 
one impregnation by the male extends over several gene- 
rations and that the ova in the exceptional cases, are 
hatched within the mother’s uterus, as in the ovo-vivipara. 
Trembley’s observations on Hydra followed these, and were 
the cause of much excitement and speculation in the scien- 
tific world. Everywhere the reproduction of lost parts, and 
the propagation of species by fissuration and gemmation 
were investigated and established as facts. Finally, three 
quarters of a century after Trembley’s discovery, the true 
ova of the compound ascidians (animals which have been 
classed with the polyps, and whose powers of gemmation 
were known), were discovered by Milne-Edwards and 
Audouin. The ova were found to produce a larva, which 
eventually settled down and gave rise to a colony. Asin 
the aphides, the ascidian sprung from an egg, was found to 
give rise, without sexual intercourse, to a number of new 
beings, and, aaa coming under the ordinary law, de- 
posited true ova. In 1819 Chamisso detected the mode of 
reproduction of ‘the biphors, and coined the expression 
“alternation of generations,” He found that the isolated 
