The Descent of Man

in some instances for their rarity in collections.
(92. See, on this subject, Mr. O.P. Cambridge, as
quoted in 'Quarterly Journal of Science,' 1868,
page 429.)
Some of the lower Crustaceans are able to propagate
their kind sexually, and this will account
for the extreme rarity of the males; thus
von Siebold (93. 'Beitrage zur Parthenogenesis,'
p. 174.) carefully examined no less than 13,000
specimens of Apus from twenty-one localities,
and amongst these he found only 319 males.
With some other forms (as Tanais and Cypris),
as Fritz Muller informs me, there is reason to
believe that the males are much shorter-lived
than the females; and this would explain their
scarcity, supposing the two sexes to be at first
equal in number. On the other hand, Muller has
invariably taken far more males than females of
the Diastylidae and of Cypridina on the shores
of Brazil: thus with a species in the latter genus,
63 specimens caught the same day included 57