smaller ones being surrounded by a row of larger ones. [Illustration: Fig. 112. Magnified pendent knob.] [Illustration: Fig. 113. Medusa with corkscrew shaped tentacles.] The second set of Hydræ (Fig. 113), are also open-mouthed, corresponding with those described above, in everything except the tentacles, which are both shorter and thicker, and are coiled in a corkscrew-like spiral. These are thickly studded for their whole length with lasso-cells. (See Fig. 113.) In the third and last set of Hydræ (Fig. 114), the mouth is closed; they have, therefore, no share in feeding the community, but receive their nourishment from the cavity of the stem into which they open. They differ also from the others in having a single tentacle instead of a cluster, and on this tentacle the lasso-cells are scattered at uneven distances (Fig. 114). The special function of these closed Hydræ is yet to be explained; they have oil bubbles at their upper end (see Fig. 111, the top Hydra), and though we have never seen them drop off, it seems natural to suppose that they do separate from the parent stock, and found new communities similar to those from which they arise. [Illustration: Fig. 114. Medusa with a simple thread-like tentacle.] The intricate story of this singular compound existence does not end here. There is still another set of individuals whose share in maintaining the life of the community is by no means the least important. Little bunches of buds, of a different character from any described above, may be seen at certain distances along the lower part of the stem. These are the reproductive individuals. They are clusters of imperfect sexual Medusæ, resembling the rudimentary Medusæ of Tubularia (Fig. 99), which are never freed from the parent stem, but discharge their contents at the breeding season. Like many other compound Hydroids, the sexes are never combined, in one of these communities; they are always either male or female, and as those with female buds have not yet been observed, we can only judge by inference of their probable character. Front what is already known, however, of Hydroid communities of a like description, we suppose that the process of reproduction must be the same in these, and that the female stocks of Nanomia give birth to small Jelly-fishes, the eggs of which become oil bubbles, similar to that with which our little community began. (Fig. 108.) [Illustration: Fig. 115. Adult Nanomia, natural size, at rest.]