[Illustration: Figs. 257, 258.] In others of this same group, however, there occur forms which show us an incipient bilateralness; and help us to see how a more decided bilateralness may arise. Sundry of the _Medusidæ_ are proliferous, giving origin to gemmæ from the body of the central polypite or from certain points on the edge of the disc; and this budding, unless it occurs equally on all sides, which it does not and is unlikely to do, must tend to destroy the balance of the disc, and to make its attitude less changeable. In other cases the growth of a large process [a much-developed tentacle] from the edge of the disc on one side, as in _Steenstrupia_, Fig. 257, constitutes a similar modification, and a cause of further modification. The animal is no longer divisible into any two quite similar halves, except those formed by a plane passing through the process; and unless the process is of the same specific gravity as the disc, it must tend towards either the lowest or the highest point, and must so serve to increase the bilateralness, by keeping the two sides of the disc similarly conditioned while the top and bottom are differently conditioned. Fig. 258 represents the underside of another _Medusa_, in which a more decided bilateralness is produced by the presence of two such processes. Among the simple free-swimming _Actinozoa_, occur like deviations from radial symmetry, along with like motions through the water in bilateral attitudes. Of this a _Cydippe_ is a familiar example. Though radial in some of its characters, as in the distribution of its meridional bands of locomotive paddles with their accompanying canals, this creature has a two-sided distribution of tentacles and various other parts, corresponding with its two-sided attitude in moving through the water. And in other genera of this group, as in _Cestum_, _Eurhamphæa_, and _Callianira_, that almost equal distribution of parts which characterizes the _Beroe_ is quite lost.