8 蒋悟生生物专业英语 第八课.docVIP

Lesson 8 Animal Development Production of Sperm and Eggs In sexually reproducing organisms males and females produce sex cells, known as gametes. These are swimming sperm in males and ova (eggs) in females. 在有性生殖的生物中，雄性和雌性产生生殖细胞，即配子。它们是雄性体内能游动的精子和雌性的卵子。 The process of sperm production, spermatogenesis, takes place in testes. The sperm originate in gonial cells (spermatogonia精原细胞) in the walls of seminiferous(输精管) tubules. Spermatocytes（精母细胞）produced by mitosis in spermatogonia divide meiotically to generate haploid spermatids精细胞. The mature sperm has a tail, a nucleus containing haploid chromosomes, and a front end with an acrosome, the storage site for enzymes that will aid fertilization. 精子产生的过程，精子发生，发生在睾丸。精子起源于输精管壁的性母细胞(精原细胞)。精原细胞有丝分裂产生的精母细胞减数分裂生成单倍体精细胞。成熟的精子有一条尾巴，一个含有单倍体染色体的细胞核，还有一个带顶体的前端，顶体是帮助受精的酶的存储场所。 Ova（n. 卵细胞ovum 的复数）, which are produced during oogenesis, are generated in gonial cells (oogonia卵原细胞;) of the female's ovaries. Oocytes(卵母细胞)then enter a stage of arrest in early meiosis. At a species-specific later point, a final ripening (ovulation) and the first meiotic division occur. A second meiotic division, followed by development of the embryo, takes place if the egg is fertilized. 卵巢在卵子发生过程中产生，产生于雌性卵巢的卵原细胞。卵母细胞在减数分裂早期进入停滞阶段。在物种特异的后期某时间点，发生最后的成熟(排卵)和第一次减数分裂。如果卵子完成受精，就会发生第二次减数分裂，接着是胚胎的发育。 Eggs vary greatly in size from species to species and have complex structures. Virtually all developing animal ova are surrounded by helper cells, either follicle（滤泡） cells or nurse cells. Depending on the species, eggs also store varying amounts of yolk, a reservoir of nutrients produced by digestive-gland cells in the mother's body. Finally, follicle cells or cells of the maternal oviduct provide protective coatings for the egg, including albumen (白蛋白egg white) and various types of outer membranes and shells. 卵的大小因物种而异，结构复杂。几乎所有发育中的动物卵子都被辅助细胞包围，要么是卵泡细胞，要么是哺育细胞。不同的物种卵也会储存不同数量的卵黄，卵黄是母体内消化腺细胞产生的营养物质的储存库。最后，卵泡细胞或母体输卵管细胞为卵子提供保护层，包括蛋白(白蛋白蛋清)和各种类型的外膜和外壳。 Frog oocyt