GENESIS, OR PARTHENOGENESIS. 443 
purpose, however, it will be sufficient to advert very briefly 
to a few of the leading points in the history of the genesis 
of animals, a history which has gradually unfolded itself to 
view and which now claims for its subject the state and 
character of a special branch of science, though it may not have 
attained to the authority and certainty of the better and longer 
known physical sciences. 
From the observation of the budding Hydra has arisen, and 
by degrees perfected itself, a doctrine of “ gemmiparous 
reproduction,” the phenomena of which received the early 
attention of zoologists and have been almost exhaustively 
investigated. The viviparous larvation of the Aphides formed 
the starting-point of the new and daily extending theory of 
Parthenogenesis. Respecting the cause of the reproduction 
of the Aphis larvae the original discoverers were divided in 
opinion. Bonnet, a believer in the doctrine of “ pre-existing 
germs,” held that each individual of the summer Aphides 
was a female which developed its own germs, and that 
the autumn eggs were nothing but imperfectly nourished 
“ germs.” Reaumur, on the contrary, held to the opinion 
that the Aphis might be an androgynous insect. But when, 
in course of time, the widely- extended occurrence of gem- 
miparous ” reproduction through the lower classes of animals 
was comprehended in its full significance, and the distinction 
between external gemmation from the surface and internal 
gemmation from a “ germ-stock ” within the creature's body 
was pronounced to be one only of local circumstance, the case 
of the Aphis was referred to the general law of internal 
gemmation ; that is to say, the successive broods of summer 
Aphides were considered to be simple “ deciduous buds.” 
The sexual condition of the Aphis first produced from the egg 
remained still a vexed question. And the recently published 
statement of Balbiani, which, if confirmed, will remove the 
phenomena of Aphis larvation from those of other animals 
under the law of Parthenogenesis, offers a suitable occasion 
for a short review of the facts and opinions urged by the 
writers who have interested themselves in the solution of this 
curious problem of organic life. 
Whatever be the differences noticeable in the forms of 
<c gemmiparous reproduction,” they all agree in exhibiting one 
striking peculiarity, namely, that the immediate product of 
the ovum is not itself the producer of ova, but that this 
function is performed by the sexual individuals which are the 
product of its non- sexual progeny. This non- sexual multi- 
plication may be repeated once or through many descents, 
but in every case a true generative act closes the cycle of 
intermediate production, and in every class of animal dis- 
vol. v. — no. xxi. 2 H 
