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[Salinan]Disalin!
Figure 1A shows an ovary fragment containing translucent previtellogenic, aswell as opaque early vitellogenic oocytes. During stage 3 (Fig. 1B), the mature ovum contains oil droplets that are evenly distributed over the yolk surface. After fertilization, the oil droplets coalesce underneath the embryo proper, which forms a blastodisc (stage 4; Fig. 1C). During stage 5 (Fig. 1D), the primitive streak is seen on top of the shield, and this appearssmaller in guppies relative toGambusia(drawing at the left). At the optic cup stage (stage 6; Fig. 1E), the eyes remain unpigmented, blood vessels of the portal system are visible in thelower part of the yolk sac, and the heart becomes perceptible as a pulsating tube. The early-eyed embryo (stage 7; Fig. 1F) is pigmented light brown, first at the dorsoanterior margin and subsequently throughout the retina. Melanophores are undetectable on the head or trunk at thisstage. During the early-eyed period, pigmentation of the eye, including the choroid, gradually increases, the pectoral fin buds emerge, and somitic as well as nonsomitic muscles differentiate. Classification of the subsequent middle-eyed, late-eyed, and very lateeyed stages (stages 8 –10; Fig. 1G–I) is based on further differentiation of the eyes, which parallels an increase in the skin pigmentation of the head and trunk. The middle-eyed embryo hasfully pigmented eyes (Fig. 1G), whereas, in the late-eyed embryo, the choroid covers most of the retina, and rays of the dorsal, ventral, and caudal fins have differentiated. The myotome consists of approximately 30 somites (Fig. 1H). During the middle-eyed stage, melanophores first appear above the midbrain and subsequently behind the midbrain– hindbrain boundary (stage 8; Fig. 1G). In the subsequent late-eyed stage, a line of dark pigmentcells appears that demarcates the horizontal midline, and the mostly stellate black pigment cells on the head increase in number, size, and density, and become more dendritic in their appearance (stage 9; Fig. 1H). Different regions of the embryo are often covered by melanophores of different shapes (Goodrich et al., 1944; Tavolga, 1949). Furthermore, paired dorsal and ventral pigment lines emerge, followed by a second, weaker horizontal line of melanophores above and parallel to the midline. Trunk pigmentation remains inconspicuous until the very late-eyed stage, when a rhombic melanophore pattern emerges between the dorsal and upper horizontal melanophore lines, and this pattern gradually develops from the dorsoanterior to the ventroposterior region of the trunk (stage 10; Fig. 1I). Melanophores and iridophores accumulate
over the lateral patches that cover the yolk. Between the very late-eyed and mature embryo stages, iridophores also differentiate on the choroid of the eyes (stage 12; Fig. 1I,K).
Simultaneous with the disappearance of the yolk, the almost rectangular flexure between the head and the trunk is gradually straightened (Fig. 1H–K). The mature embryo has resorbed completely its yolk and retracted the yolk sac. Finally, the follicle ruptures before birth (stage 11;
Fig. 1K)
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