. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDRA EMBRYOGENESIS Table III 357 iHi during embryogenesis Stage Epithelial cells Large interstitial cells Small interstitial cells Nematoblasts + Nematocytes Secretory Neurons cells Blastula 76 Gastrula 315 — — — — — Cuticle formation 400 — — — — — Cuticle (40 h) 370 — — — — — Cuticle (fid) 440 — — — — — Cuticle (1 1 d) 420 140 25 — — — Bilayer 3000 1830 1230 70 40 Hatchling(0-5 ID 2830 1470 1640 370 70 160 Hatchlmg(2-20h) 2830 1390 1730 1480 310 340 Data for epithelial cells are from Table I. The number of cells of the int
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDRA EMBRYOGENESIS Table III 357 iHi during embryogenesis Stage Epithelial cells Large interstitial cells Small interstitial cells Nematoblasts + Nematocytes Secretory Neurons cells Blastula 76 Gastrula 315 — — — — — Cuticle formation 400 — — — — — Cuticle (40 h) 370 — — — — — Cuticle (fid) 440 — — — — — Cuticle (1 1 d) 420 140 25 — — — Bilayer 3000 1830 1230 70 40 Hatchling(0-5 ID 2830 1470 1640 370 70 160 Hatchlmg(2-20h) 2830 1390 1730 1480 310 340 Data for epithelial cells are from Table I. The number of cells of the interstitial cell lineages are calculated from the numbers of epithelial cells and the ratios of interstitial cell lineage cell type to epithelial cells from Table 11. dergo only another two to three divisions. And. if the minimum hatching time is about 13-14 days, about ten cell divisions occurred in the first day, and the remaining two to three occurred in the last 12-13 days. The outer layer of blastomeres formed at gastrulation will give rise to the ectoderm. After ingression is com- plete, these cells still contain nurse cells, although they are fewer and mostly located near the basal portions of the cells (Fig. 39). In animals whose hatching time was not artificially reduced, a distinct change occurs by 6 days postfertilization. The outer layer next to the cuti- cle consists of a layer of squamous cells devoid of nurse cells (Fig. 41). In addition, the morphology of the nuclei of these cells changes from the amorphous nucleus of a blastomere to the clear nucleus, characterized by a prom- inent nucleolus, of an adult epithelial cell. This layer most likely arose from blastomeres of the outer layer un- dergoing a division parallel to the surface and giving rise to the squamous cells next to the outer cuticle and deeper, somewhat larger, cells that contain nurse cells. The next distinct change in this layer occurs 2 days before hatc
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
