88 
BRITISH APHIDES. 
oviparous and that the converse also is true. Kyber, 
many years ago, showed that some species of Aphis 
carry their viviparous character throughout a period 
of seven years, so that this mode of reproduction, 
without union of sex, has been considered by Huxley 
to be, in a manner, almost unlimited.” 
Every new discovery of the perfect sexes of Aphides 
and other living forms is of interest, as adding evidence 
to the likelihood of Nature’s recurrence to normal 
phenomena, without which recurrence, probably, no 
species can be permanent in time. A parallelism 
surely may be traced in the vegetable world. Horti- 
culturists and pomologists recognise that there is a 
limit to propagation by simple grafts or buds, at least 
they see that choice varieties die out, and perhaps 
never can be reproduced. Recurrence must be made 
to seed when new characters may appear. So, also, 
doubts must rise as to the permanence of any animal 
life without some occasionally renewed seminal influ- 
ence. Centuries, however, we might conceive possible 
in certain instances to elapse before the close of a cycle. 
Apposite to this Mr. Bentham remarks that, ‘‘ as 
Von Siebold, Leuckardt, and others have traced 
back worms and other parasites through various 
strange wanderings to an egg derived from a parent 
similar to itself, so a plant may throw off bulbs, 
but these sooner or later give rise to seeds or spores 
which develope into the original form. A Polype 
may produce a Medusa or a Pluteus or an Pcliino- 
derm, but the Medusa and Ecliinoderm give rise to 
eggs which produce Polypes or Medusce ; they are there- 
fore only stages in the cycle of life of the species.”^ 
Nevertheless the fact remains of much interest, that 
myriads of Aphides and also of other creatures are 
brought yearly into existence by a peculiar develop- 
ment ; and that the males occur only at such remote 
intervals that their action seems to exist at a minimum. 
Address to tlie Linn, Societj, Ma^, 1871, 
