THE ENTOMOLOGISTS 
WEEKLY INTELLIGENCER. 
No. 161.] SATURDAY, OCTOBER 29, 1859. [Price Id. 
GEOMETRICAL PROGRESSION. 
It is well known that a new species 
of silk-worm has lately been introduced 
into Europe, the Bombyx Cynthia, of 
which the larva feeds on the leaves of 
the castor-oil plant ( Ricinus communis). 
The culture of this new silk-worm is 
at present in a sort of experimental 
state, but it has yet attracted consider- 
able attention, and a pamphlet has 
lately been published in Germany, 
extracts from which have recently ap- 
peared in the ‘ Journal of the Society 
of Arts.’ 
Unlike the true silk-worm ( Bombyx 
Mori), of which only one generation 
annually is to be expected in the 
climate of Europe, the Bombyx Cynthia 
goes through its whole series of changes 
in six weeks, so that it would be 
possible to obtain eight broods in the 
year, if only the larvm be well supplied 
with food. 
The author of the German pam- 
phlet, Herr Ernst Kauffman n, has 
made a calculation as to the number 
of descendants which might be ob- 
tained from a single pair of the 
Bombyx Cynthia in the course of 
twelve months. 
“ The number of eggs laid by the 
female Cynthia seldom exceeds 300, 
but it will not be found in practice 
that from every egg laid a cocoon 
will be produced. The common silk- 
worm loses, on an average, in each 
brood from one-fourth to one-third of 
the original number. If we assume 
the highest of these as the proportion 
for the Ricinus silk-worm, this will 
leave 100 couples as the first produce 
of the original pair. At the end of 
the year the descendants of this pair 
will reach to no less a number than 
ten thousand million million couples, 
and the eggs of these latter will 
amount to the enormous sum of two 
million million million.” 
“ Here,” says the author of the Re- 
port, “ breath absolutely fails me, and 
I am happy to have done at length 
with enumerating the posterity of these 
two moths.” 
He then calculates that 3,300 empty 
cocoons are amply sufficient to yield 
one pound of silk, but even allowing 
4,000, this would give 500 billion 
pounds of silk as the entire product of 
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