In external form and appearance the Hydrozoa exhibit such striking differences that there would seem at first sight to be little in common between the more divergent members of the group. Nevertheless there is no other class in the animal kingdom with better marked characteristics, or with more uniform morphological peculiarities underlying the utmost diversity of superficial characters.
HYDROMEDUSAE, a group of marine animals, recognized as belonging to the Hydrozoa by the following characters.
Sub-class Hydromedusae (Hydrozoa Craspedota).
Cylindrical or tapering from The numbers in square brackets  refer to the bibliography at the end of this article; but when the number is preceded by the word Hydrozoa, it refers to the bibliography at the end of the articl Hydrozoa.
The budding of this medusa has been worked out in detail by Chun (Hydrozoa, ), to whom the reader must be referred for the interesting laws of budding regulating the sequence and order of formation of the buds.