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四、性反转 (一)鱼类的性别 自然界的鱼类性别多种多样,有些种类为雌雄异体,其外形和体色都明显不同;有些种类是雌雄同体,或雄性先成熟或雌性先成熟,人们所熟知的黄鳝即是先雌后雄的鱼类。 相似文献
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鸡线虫病是由线形动物门线虫纲中的线虫所引起。线虫外形一般呈线状、圆柱状或近似线状,两端较细,其中头端偏钝,尾部偏尖。雌雄异体,一般是雄虫小,雌虫大,雄虫的尾部常弯曲,雌虫的尾部比较直。大小差异很大,从1毫米至1米以上,内部器官位于假体腔内。线虫主要寄生于鸡的小肠, 相似文献
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黄粉虫的饲养与应用 总被引:3,自引:0,他引:3
1黄粉虫的生物学特征黄粉虫既是一种经济昆虫,又是一种仓库害虫,属昆虫纲鞘翅目拟步行科粉甲属,幼虫体长28~32毫米,成虫体长约15毫米,雌雄异体,发育经过卵、幼虫、蛹、成虫4个阶段,属于完全变态昆虫。在我国,黄粉虫主要分布于黑龙江、辽宁、甘肃、河北、山东和四川等地。在27℃、相对湿度70%条件下,黄粉虫完成1个世代约需48天,卵期4~7天,幼虫期25~38天,蛹期6~8天,成虫卵前期4~5天,产卵可持续50天,寿命可达60天左右。通过对黄粉虫繁殖过程的测量分析,黄粉虫产卵的临界温度为15℃,产卵最适温度为25~33℃,成虫从羽化15天开始进入产卵盛期… 相似文献
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香螺雄性生殖系统的显微结构研究 总被引:6,自引:0,他引:6
香螺雌雄异体。雄性生殖系统由精巢和生殖导管构成,生殖导管可根据各段的形态和功能分为贮精囊、输精管和阴茎。生精小管内有处于不同发育时期的初级精母细胞、次级精母细胞、精子细胞。由生殖腺排入生殖导管的,不具有活动能力。输精管壁有丰富的腺细胞构成,起前列腺的作用.为精子提供营养。精于由头部和尾部构成,具有较长的中段,螺旋线粒体鞘内中央为9 2型轴丝,末段糖原颗粒包围中央轴丝。 相似文献
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Female Plant Types of Ginkgo biloba L. in China 总被引:1,自引:0,他引:1
Ginkgo biloba is a dioecious and unique species within Ginkgo family and Ginkgo genus, but it shows a big variability. From 1950s, resources of female plants in China were investigated and collected, and the seed anatomical structure and morphological characters at different development stages were observed. According to the shape, length, width and thickness of ovule bracket and seed stone, as well as the characteristics of both sides and top of the stone, the female plants of Ginkgo biloba have been divided into five types, long-stone, Buddha-finger, horse-bell, mume-stone and round-stone. In addition, the important cultivars belonging to different types were also determined. The stone weight, index of stone shape, and contents of dry matter, amylose,amylopectin, starch, rough protein, soluble sugar and hydrocyanic acid in seed kernel of each type were measured, and the qualities of seed stone were appraised, which lays a foundation for the improvement and utilization of female plant resources in Ginkgo biloba. 相似文献