. A manual of zoology. Zoology. HYDROZOA 211 The lack of sexual organs, which distinguishes most marine species from Hydra, is due to the fact that sexual individuals of special form are produced from the colony by budding. These, the meduste, may separate early from the colony and swim freely. A medusa (figs. 175, 176) has the form of a dome-like or disc-like bell and consists chiefly of very watery jelly. The bell or umbrella of the medusa is covered on both its surfaces— the concave or subumbrella, the convex or exumbrella—with ectodermal epithehum. At the margin of the bell the ectoderm is
. A manual of zoology. Zoology. HYDROZOA 211 The lack of sexual organs, which distinguishes most marine species from Hydra, is due to the fact that sexual individuals of special form are produced from the colony by budding. These, the meduste, may separate early from the colony and swim freely. A medusa (figs. 175, 176) has the form of a dome-like or disc-like bell and consists chiefly of very watery jelly. The bell or umbrella of the medusa is covered on both its surfaces— the concave or subumbrella, the convex or exumbrella—with ectodermal epithehum. At the margin of the bell the ectoderm is produced into a. Fig. 174. Fig. 173.—Campanularia geniculata. eh, ectoderm; en, entoderm; p, perisarc, ex- panded around hydranth to a hydrotheca; s, supporting layer. Fig. 174.—A bit of ilillepora alcicornis*, enlarged (after Agassiz). two-layered sheet with a central opening, the velum or craspedon (fig. 175, B, v) of systematic importance, since these medusas are often called Cras- pedota. Tentacles (usually 4, 8, or multiples in number) also arise from the edge of the bell just outside the velum. Comparable to the tongue of the bell or the handle of the umbrella is the 7naivubrium, hanging from the highest point of the subumbrella and bearing the mouth at its tip. It contains the chief digestive space, from which radial canals run on the subumbrellar surface to a ring canal in the margin of the umbrella. The radial canals are usually four in number, but in some species the number is increased during growth even to a hundred or more. Manubrium and canals are lined by entoderm, which also extends into the tentacles and forms their 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
Size: 1883px × 1327px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
