排序方式： 共有39条查询结果，搜索用时 15 毫秒
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行蜕壳式增长的节肢动物个体发育及性双形特征的研究必须建立在其化石种群结构的恢复之上。简单的数理统计是揭示其种群结构特征的钥匙:鉴别是否属正常化石种群,确定蜕壳期数,解释早期幼壳高死亡率与其化石低保存牢的统一。高肌虫个体发育常表现为六至七期明显的蜕壳阶段,蜕壳期间壳体增长率常在性成熟期有显著的减小趋势。物种的正确鉴定及性双形特征的辨识也只有通过个体发育研究才能得到合理的解决;物种在个体发育过程中表现出来的性伏变化,为研究谱系的演化趋向提供重要依据。这种数理统计方法无疑对三叶虫、介形虫等其他节肢动物的个体发育及性双形研究也完全适用。 相似文献
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YU ChangMin 《中国科学D辑(英文版)》2007,50(12)
Based on studying the ontogenetic development of Calceola sandalina in the Early Devonian Yukiang Formation from Guangxi Zhuang Autonomous Region, South China, it is for the first time to issue the evidence indicating the existence of sexual dimorphism in Calceola sandalina. The new discovery will add important data on sexual dimorphism throughout the non-colonial fossil metazoan, and it also may throw lights on studying the taxonomy and phylogeny of Calceola sandalina and its relevant taxa. 相似文献
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Metoicoceras 《Cretaceous Research》2000,21(6):845
Species of the ammonite genus Metoicoceras are not generally strongly differentiated with respect to coiling and ornament. The present study addresses the problem of how well purely visual (subjective) identification succeeds in identifying taxonomically and hence evolutionarily relevant differences between forms. Multivariate statistical analysis, based on coiling, standard dimensions of the conch and ornamental properties, indicates that quantitative procedures reproduce traditional methods to a conspicuous degree, with the added advantage of objective repeatability. Additionally, uncertain phylogenetic relationships could be resolved by appropriate methods of multivariate statistical analysis and possible new information on dimorphism in the conch was obtained. 相似文献
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部分水生经济动物具有性别二态性,这种特性与养殖品质、商业价值相关。与哺乳动物不同,水生动物不具有明显的性征,在育种时难以识别亲本性别,会造成额外的劳动力和培育成本。该文主要围绕水生经济动物性别遗传基础及其鉴定方式,综述了水生经济动物的性别二态现象、常见的性别鉴定方式以及决定基因,以期为种质资源保护和良种选育提供理论参考。 相似文献
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采用室内培养和野外实地观测的方法,研究了鼠尾藻的生长发育和有性生殖过程,并在此基础上进行了有性生殖人工育苗实验。结果表明,鼠尾藻在海水温度高于22℃时,生殖托开始发育,海水温度超过23℃以后,生殖托的生长速度加快,海水温度超过24℃时,生殖托生长速度最快并迅速成熟,在海水温度达到26℃时,观察到了卵的集中排放挂托现象。鼠尾藻卵的排放较为齐整且有一定的先后顺序,生殖托基部的卵最先排出,中部次之,最后是顶部,雄托排精时间要稍晚于雌托排卵时间。受精卵大约在受精1h后进行第一次细胞分裂,分裂面与长轴垂直,大约2h后进行第二次分裂,下端细胞的分裂面平行于第一次分裂方向,而上端细胞的分裂面则垂直,随后大约每2—4h细胞分裂一次。从卵挂托到幼胚脱落一般需要24—48h。观察发现,生殖窝不仅存在于生殖托上,在部分生殖枝上也有分布。在鼠尾藻的人工育苗的实验中,胚苗在苗帘上的生长状态良好。 相似文献
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Yoshikazu Hasegawa Yojiro Taketani Hajime Taru Osamu Sakamoto Makoto Manabe 《Island Arc》1994,3(4):513-521
Abstract Upon studying the well preserved skulls referred to Paleoparadoxia tabatai from Japan, the short and low skull of the Yanagawa specimen requires an explanation. Six cranial and dental characters lead us to suggest that the Yanagawa individual is a female while the Izumi, Ohnohara, and Itsukaichi skulls are male. The important characters in the Yanagawa skull are its shortness and shallow depth, less pronounced sagittal and nuchal crests, smaller zygoma, and the small dentition with especially poorly erupted canines, most of which are indicative of weak masticatory musculature. 相似文献