. Text-book of embryology. Embryology. 488 INVEETEBEATA CHAP. passive stretching of the ectoderm, but rather because the pressure of the growing tip of the rod stimulates the ectoderm to increased growth. If the larva be exposed to unfavourable conditions, such as lack of oxygen, etc., the ectoderm shrinks, and the pointed tip of the calcareous rod projects as a naked spine, so that if there were any- stretching of the ectoderm the spine would immediately pierce it. As the anterior vacuolated crest disappears, another, consisting of. Fig. 375.—Ventral views of young larvae of Ophiothrix fragil
. Text-book of embryology. Embryology. 488 INVEETEBEATA CHAP. passive stretching of the ectoderm, but rather because the pressure of the growing tip of the rod stimulates the ectoderm to increased growth. If the larva be exposed to unfavourable conditions, such as lack of oxygen, etc., the ectoderm shrinks, and the pointed tip of the calcareous rod projects as a naked spine, so that if there were any- stretching of the ectoderm the spine would immediately pierce it. As the anterior vacuolated crest disappears, another, consisting of. Fig. 375.—Ventral views of young larvae of Ophiothrix fragilis. (Original.) A, larva, two and a quarter days old. B, larva, three days old. a, anus ; , antero-lateral arm ; , antero-lateral rod; &.r, body rod; , longitudinal ciliated band ; int, intestine; , left coelomic sac; , postero-lateral arm; , postero-lateral rod; , post-oral arm; , post- oral rod ; , right coelomic sac; H, stomach ; stom, stomodaeum. a precisely similar ridge of ectoderm, makes its appearance at the posterior pole of the larva, and this second crest persists through the entire period of larval development. This we may term the posterior vacuolated crest. The purpose of these crests seems to be to diminish the specific gravity of the larva, and so balance the increase in weight due to the development of calcareous matter. The posterior rod of the calcareous star on each side meets its fellow just above this posterior crest. The lower ends of these "body-rods" bifurcate, and, by the meeting of the forks. 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
Size: 1571px × 1591px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
