. Comparative anatomy and physiology. Chap. III.] JELL Y- In the third group we have those free- swimming colonies to which reference has already been made as examples of the highest form of division of labour : they are called the Siplioiiopliora, and Velella, Diphyes, Physalia, and Physo- phora (Fig. 12) belong to this group. In the second great division of the hydrozoa we have the forms which are best known as the Medusae, or jelly- fishes pair excellence. With one exception, they all pass through a stage which, at first somewhat hydriform in appearance (Scypliis- toma-stag
. Comparative anatomy and physiology. Chap. III.] JELL Y- In the third group we have those free- swimming colonies to which reference has already been made as examples of the highest form of division of labour : they are called the Siplioiiopliora, and Velella, Diphyes, Physalia, and Physo- phora (Fig. 12) belong to this group. In the second great division of the hydrozoa we have the forms which are best known as the Medusae, or jelly- fishes pair excellence. With one exception, they all pass through a stage which, at first somewhat hydriform in appearance (Scypliis- toma-stage), is re- markable for under- going transverse di- vision ; each of the segments so formed separates and forms an independent medusa. When adult they are always medusiform in appearance, and, as they rarely have a velum to their disc, they are1 <*---, TIT,. Fig. 12.—PTiysophora hydrostatica. a, Air-bladder ; m, nectocalyx; g, gener- ative persons; «, nutrient persons (in the form of sucking tubes); t, tentacu- lar persons. (After Cuvier.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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