 Fig. 107. Young Nanomia; magnified. |  Fig. 108. Young Nanomia with rudimentary Medusæ. |  Fig. 109. Young Nanomia, older than Fig. 108. |
 Fig. 110. Heart-shaped swimming bell of Nanomia; magnified. | ||
Fig. 111. Cluster of Medusæ with tentacles having pendent knobs.
Besides these locomotive members, the community contains three kinds of Hydræ arising as buds from the primitive Hydra below the swimming bells, the latter remaining always nearest the oil bubble at the top, while the first Hydra, the founder of the community, in proportion as the new individuals are added, is gradually pushed downward, and remains always at the end of the string, the stem of which is formed by the elongated neck of the primitive Hydra. All the three sets of Hydræ have certain features in common, while they have other distinguishing characteristics marking them as distinct individuals. They are all accompanied by triangular shields ([Fig. 111]), arising with them at the same point on the parent stem, and all are furnished with tentacles hanging down from the summit of the Hydra at the side opposite the shield. These facts are important to remember, since we shall presently perceive, upon analyzing their parts, that these Hydræ have a close homology to the Hybocodon. The tentacles differ in structure as well as in number for each kind of Hydra. Having shown in what characters they agree, let us now take each set individually, and see what differences they present.