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(一)眼的进化一般无脊椎动物的眼都是由被复上皮(表皮的外胚层)分化出来的。人和脊椎动物的眼就与无脊椎动物不同,它们是从神经外胚层发生的,脑也是由神经外胚层形成的,眼也就是由脑生长出来的突起。在胚胎发育时期,前脑泡外侧壁发展成一对突起——原始眼泡。原始眼泡内外皮生长,并借一个中空的短柄与第三脑窒相联,眼泡的前壁变厚,同时又渐渐向泡内凹陷下去,形成有双重壁的杯状体,随着眼杯向外皮接近,在外胚层中形成了陷入眼杯内的肥厚部分,后者分离出来形成眼球水晶体的胚芽,从眼杯的内层形成网膜,由外层形成网膜的色素层。眼杯的空腔充满了胶质的玻璃样体。连接眼杯与脑的中空的短柄也充满了从网膜长到脑的神神经维。这样看来,
(A) the evolution of the eye In general, the eyes of invertebrates are complex epithelial (epidermal ectoderm) differentiation out. The eyes of humans and vertebrates are different from those of invertebrates. They occur from neuroectoderm. The brain is also formed by neuroectoderm. The eye is the protuberance that grows from the brain. During embryonic development, the outer lateral wall of the forebrain develops into a pair of protuberances - the primitive eye. The original eye inner and outer skin growth, and by a hollow short handle and the third brain choking associated with thickening of the anterior wall of the eye, while gradually sinking into the bubble to form a double wall of the cup-shaped body, with the eye cup to Outer skin close to form in the ectoderm plunged into the ophthalmic hypertrophic part, the latter separated out to form the embryo of the eye lens, the inner layer from the eye cup to form an omentum, the outer layer of retinal pigment layer. The cavity of the eye cup is filled with a glial glass-like body. The hollow stub that connects the eye cup to the brain is also full of neurons that grow from the retina to the brain. In this way,