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关键词： MOLECULAR PHYLOGENY   12S RIBOSOMAL-RNA   CYTOCHROME-B   FOSSIL RECORD   RHIPIDISTIANS   TETRAPODS   LUNGFISH   COELACANTH   RAY-FINNED FISH   MORPHOLOGICAL PARALLELISMS   LIVING FOSSILS   ANCESTOR  

摘要： Meyer and Wilson's (1990) 12S rRNA phylogeny unites lungfish and tetrapods to the exclusion of the coelacanth. These workers also provide a list of morphological features shared in common between modem lungfish and tetrapods, and they conclude that these traits were probably present in their last common ancestor. However, the exquisite fossil records of the abundant extinct lungfishes and rhipidistians show that at least 13 out of Meyer and Wilson's 14 supposed ancestral traits were not present in the last common ancestor of lungfishes and tetrapods. Using extant taxa to infer ancestral morphologies is fraught with difficulties;just like molecular sequences, ancestral character states of morphological traits may be severely over-printed by subsequent modifications. Modem lungfish are air-breathing nonmarine forms, yet their Devonian forebears were marine fish that did not breathe air. Fossils dating from the time of origin of tetrapods in the Devonian offer the only hope of understanding the morphological innovations that led to tetrapods;morphological analysis of the "living fossils," the coelacanth and lungfish, only lends confusion.

关键词： TESTIS   SPERMATOGENESIS   KINETICS   MALE GERM CELLS, TOXICOLOGY   MODELING   COMPUTER PROGRAM  

摘要： A computer program called Stages was written to aid the tracking of germ cells and stages forward and backward through time in the cycle of the seminiferous epithelium. The program incorporates the basic kinetics of spermatogenesis in the rat, mouse, hamster, guinea pig, dog, rabbit, bull, stallion, ram, boar, quail, monkey, and man. The program is flexible and permits the user to alter the cycle duration time and the frequency of each stage. Compiled for use on personal computers and available on floppy disks free of charge, Stages is menu-driven and requires no knowledge of programming. The program was tested using published data of testicular toxicity and vitamin A synchronization of stages. In general, predicted cell types were similar to those observed;discrepancies between observed and predicted data are discussed. When cycle duration time was changed, predicted data for stage synchronization coincided with the observed data. This program will improve the speed and accuracy of studying factors that affect spermatogenesis. By using Stages, it is possible to predict the target cell types in a toxicity study and to track affected cells over long periods of time. Predicted cell types may also indicate which cells to examine biochemically as well as morphologically in subsequent experiments. The program will also be useful to beginning students learning the complex patterns of cellular associations and the progression of germ cells in the cycle of the seminiferous epithelium.

关键词： FOSSILS  

摘要： The fossil record offers the only direct evidence of extinct life and thus has figured prominently in considerations of evolutionary patterns. But the incomplete nature of the fossil record has also been emphasized in arguments that fossils play only a secondary role in the recovery of phylogenetic histories based on extant taxa. Although these criticisms recently have been countered, there is no general understanding of the correspondence between the fossil record and phylogeny. An empirical survey of recently published studies suggests no basis for assuming that the stratigraphic occurrence of fossils always provides a precise reflection of phylogeny. Nevertheless, our survey of a sample of taxa shows a tendency for positive correlation between age and clade rank and, hence, a degree of correspondence between phylogenetic pattern and the paleontologic record.

关键词： 动物试验   血吸虫病   生物学   日本  

摘要： 在研究血吸虫病的治疗药物时,需要进行疗效考核,一般采用动物人工发病,定量接种血吸虫尾蚴,待粪孵阳性后,进行治疗,隔一定时间后进行解剖并用静脉冲洗法收集虫体计数,作为考核疗效的依据。

关键词： 哺乳动物   一氧化氮  

摘要： 一氧化氮(NO)是一种不寻常的信使分子,化学本质非常简单,是一种难溶于水的气体。但是,像氧和二氧化碳一样,NO能以扩散方式,自由跨越细胞膜,因而其作用不受释放、摄取等机制的直接调控。再者。

关键词： CRUSTACEA   ECOLOGY   HISTOPHAGY   LIFE CYCLES   PREDATION  

摘要： The histophagous apostome, Vampyrophrya pelagica, occurs on calanoid copepods in North Carolina. Its life cycle has two pathways: one when the copepod host is injured;the other when the host is ingested by an invertebrate predator. The ciliate, immediately after encysting on a copepod, metamorphoses to a feeding stage. When its host is injured or ingested by a predator, it excysts enters the wound and ingests the host's cytoplasm. In the single-host life cycle, after feeding, the ciliate encysts within the cadaver;in the two-host life cycle, after feeding it encysts upon a substrate. Encysted cells divide into 2-32 migratory tomites. Freed tomites are motionless in the water column until the water is disturbed, at which time they spring in the direction of any vibration, which many times results from a feeding copepod. Tomites select specific hosts, since not all species of copepods are infested. We hypothesize that the single-host life cycle yields many tomites that heavily infest hosts at random, and passage through the predator (two-host life cycle) results in fewer, but more widely dispersed tomites that are released continuously. The two-host life cycle is facultative for the individual, but may be obligate for the continuation of the species.

关键词： 医学科学   医疗设备   生物测定   外科植入物   动物保护   实验室动物   外科设备  

标准号: ISO 10993-2-1992

摘要： Specifies minimum requirements for the use of animals in biological testing. Is also intended to establish guidelines which allow the scientist to respect life in general, to reduce the number of animal experiments and the number of animals used in experiments, to minimize suffering and maintain the quality of life of the animals used in the experiments. Applies to the experimentation performed on vertebrates.