. The biology of the frog . FlG. 21. —Transverse section through the middle of a frogs embryo. CH,notochord; E, ectoderm ; M, mesoderm ; AG, neural groove; NP,neural plate ; T, mesenteron ; Y, yolk cells. (After Marshall.) body cavity. It is at first small, but as development proceeds,it widens out more and more. The cells just above the mid-dorsal wall of the archenteronform a thickening which soon becomes marked off sharplyfrom the mesodermic layers on either side and the wall ofthe archenteron below. This thickening is the beginningof the notochord, a structure forming the beginning of the
. The biology of the frog . FlG. 21. —Transverse section through the middle of a frogs embryo. CH,notochord; E, ectoderm ; M, mesoderm ; AG, neural groove; NP,neural plate ; T, mesenteron ; Y, yolk cells. (After Marshall.) body cavity. It is at first small, but as development proceeds,it widens out more and more. The cells just above the mid-dorsal wall of the archenteronform a thickening which soon becomes marked off sharplyfrom the mesodermic layers on either side and the wall ofthe archenteron below. This thickening is the beginningof the notochord, a structure forming the beginning of the ,,s THE BIOLOGY OF THE FROG vertebral column, and occurring in the embryo, when notalso present in the adults, of all vertebi-te animals. It NO. FIG. 22. — Transverse section through a frog embryo before the closure ofthe medullary or neural folds. C, ccelom or body cavity; CH, noto-chord; EE, epidermic layer of ectoderm ; EN, nervous layer of ecto-derm ; M, mesoderm ; ME, outer or somatic mesoderm ;. A/H, inner orsplanchnic mesoderm; NC, neural groove; ND, dorsal root of spinalnerve; NS, spinal cord; T, archenteron; W, liver diverticulum; Y,yolk. (After Marshall.) is always the first part of the skeleton to make its appear-ance in the embryo, as it was the first part to appear in theevolution of the race. Whether in the frog it is entodermic V THE DEVELOPMENT OF THE FROG 99 in origin, as it certainly is in some of the Amphibia and inmany other vertebrates, or whether, as maintained by Mor-gan, it is developed from the mesoderm, is a matter aboutwhich there is a difference of opinion. Miss H. D. King lhas recently studied the formation of the notochord in Bufolentiginosus and Rami palustris, and has come to the con-clusion t
Size: 1410px × 1773px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1900, bookdecade1900, bookidbiologyoffrog1907holm
