Considering the wide differences between the two groups in the size and external characters, and in the mode of life, including the mode of feeding, it is indeed surprising that in every important organ the two groups should show a fundamental morphological identity.
Yeasts was by studying morphological differences with the aid of the microscope.
Since, however, medusa-colonies occur only in one group, the Siphonophora, and divergent views are held with regard to the morphological interpretation of the members of a siphonophore, only the first three of the above sub-divisions of hydromedusa morphology will be dealt with here in a general way, and the morphology of the Siphonophora will be considered under the heading of the group itself.
The special property of the medusa is the umbrella, distinguishing the medusa at once from other morphological types among the Coelentera.
Many views have been put forward as to the morphological relationship between the two types of person in the Hydromedusae.