In some of the genera parthenogenetic propagation is carried to such an extent that of the familiar Cypris it is said, " until quite lately males in this genus were unknown; and up to the present time no male has been found in the British Islands " (Brady and Norman, 1896).
On the other hand, the ejaculatory duct with its verticillate sac in the male of Cypris and other genera is a feature scarcely less remarkable.
Dr Bather justifiably anticipates further discoveries, but if, already in Silurian as in modern times, the members of these families had to pass through nauplius and cypris stages to maturity, there is one " enormous gap " between them and the common ancestor of the crustacean class that will not be easily filled.