. Zoology : for students and general readers . Zoology. LAIiV^ OF ANNELIDS. 333 been studied, the eggs are probably laid in masses between tide-marks, and the young, when hatched, swim freely on the surface of the sea. The eggs of other worms are carried about in lateral pouches. The germ undergoes a cleavage phase and a gastrula stage. We have observed, in Salem harbor, the development of Pohjdora (probably P. ciliatum Clap.) which may be found in August, in all stages, on the. Fig. 153.—^, earliest observed Btage of Polydora; B, Cephalala stage ; Pand D, later stages.—Author del. surface of
. Zoology : for students and general readers . Zoology. LAIiV^ OF ANNELIDS. 333 been studied, the eggs are probably laid in masses between tide-marks, and the young, when hatched, swim freely on the surface of the sea. The eggs of other worms are carried about in lateral pouches. The germ undergoes a cleavage phase and a gastrula stage. We have observed, in Salem harbor, the development of Pohjdora (probably P. ciliatum Clap.) which may be found in August, in all stages, on the. Fig. 153.—^, earliest observed Btage of Polydora; B, Cephalala stage ; Pand D, later stages.—Author del. surface of the water. When first observed (Fig. 153, A) the body was spherical, with a short, broad intestine, and two sets of large locomotive hristles. It then passed into the cephalula state, the head clearly indicated and forming a large hood. This stage is seen at B, which represents the under side of the cejihalula, the mouth being situated be- tween the two large ciliated flaps (like the velum of larval mollusks) of the hood; the body is now segmented, with a third set of bristles and a band of cilia on the penultimate segment; afterwards as at G, dorsal view, additional rings are present; the eyes are distinguishable, and there are two more sets of bristles. The new segments are, as usual in all. 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 Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
Size: 1621px × 1542px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
