. Text-book of embryology. Embryology. 540 INVERTEBEATA CHAP. of the mother, and here they are fertilized. They develop veiy rapidly; the segmentation of the egg and formation of the layers is exactly like what it is in Synapta digitata. The embryo, however, never develops either the folded ciliated band of the Auricularia or the transverse bands of the pupa; it is an oval organism uniformly ciliated all over. The stomodaeum arises on the ventral side, and becomes displaced to the left and then to the anterior pole. The larval anus disappears early, and the anus is re-formed later in developme
. Text-book of embryology. Embryology. 540 INVERTEBEATA CHAP. of the mother, and here they are fertilized. They develop veiy rapidly; the segmentation of the egg and formation of the layers is exactly like what it is in Synapta digitata. The embryo, however, never develops either the folded ciliated band of the Auricularia or the transverse bands of the pupa; it is an oval organism uniformly ciliated all over. The stomodaeum arises on the ventral side, and becomes displaced to the left and then to the anterior pole. The larval anus disappears early, and the anus is re-formed later in development. The genital organ arises as a thickening of the. Fro. 401.—Pupa of Synapta digitata in two stages of development. (After MetschnikofF.) A, before tlie buccal tentacles have been protruded from the atrinm; note the five transverse ciliated bands. B, after the buccal tentacles have been protruded from the atrium; note the four transverse ciliated bands. Letters as in previous figure and in Fig. 398. In addition, at, atrium, larval stomodaeum; , rudiment of buccal skeleton ; ot, rudiment of otocyst; Pol, rudiment of Polian vesicle; , stone-canal. epithelium covering the right hand side of the mesentery carrying the stone-canal, from where the right horn of the left posterior coelom ivipinges on the anterior coelom; the enlarged cells burrow into the gelatinous substances of the mesentery, there form a spherical mass which grows out into the genital tubes, and later forms its own duct leading to the exterior. Beyond all doubt the process of the development of the genital organs is the same in Synapta digitata. Stages in the development of the genital organs of Gucuynaria glacialis have been observed by Mortensen, who confirms Clark's account (190-1:). The spot where the genital cells make their appearance is therefore the same in. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - co
Size: 1921px × 1300px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
