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801.
The daughter sporocyst of Gorgoderina vitelliloba develops attached to the gills of its molluscan host, Pisidium. It has a conical attachment structure at one end of its body through which the birth pore opens. Cercariae emerge through the birth pore, their passage being apparently lubricated by copious secretions from the stylet glands. Only after emergence does the anterior tail chamber envelop the cercarial body to form the typical cystocercous cercaria. When sporocysts were freed from gill tissue and maintained in vitro, cercariae failed to escape from the sporocyst and several encysted, in situ. It is suggested that if this occurred naturally a different host range would be encountered and the long term result might be the evolution of a new species. 相似文献
802.
A fossil specimen ofMesopithecus pentelici
Wagner, 1839, from the Pikermi paleontological assemblage and currently housed at the Geological Museum of the Earth Sciences Department
of the University of Turin, is described herein. The left mandibular ramus displays dental features which permit us to assign
it to a young female individual. Anatomical patterns are discussed and are compared with other similar remains of more recent
discovery. 相似文献
803.
The genera Raabena and Pararaabena (Ciliophora, Entodiniomorphida, Blepharocorythidae) were monospecific, and their type species are Raabena bella Wolska, 1967 and Pararaabena dentata Wolska, 1968. They have been found in Asian elephants and closely resemble each other: ovoid and laterally compressed body; non-retractable adoral ciliary zone; funnel-shaped vestibulum; three non-retractable somatic ciliary arches. Furthermore, the positional relationship between the vestibular ciliary zone and the anterior dorsal ciliary zone identifies Raabena and Pararaabena: these two ciliary zones are connected in Raabena while they are separated in Pararaabena. While investigating entodiniomorphid ciliates of Asian elephants, the author often encountered ciliates similar to Raabena bella but with a sinuous body or with a small body and ciliates similar to Pararaabena dentata but with a slender body or with no or two caudal lobes. In this study, their general morphology and infraciliature were compared to R. bella and P. dentata to know whether they are new species or morphological variations in a species. As a result, the present study redescribed R. bella and P. dentata, and described R. sinuosa n. sp., R. bellafilia n. sp., P. gracilis n. sp., and morphotypes of P. dentata. 相似文献
804.
Although individual neurons can be intrinsically oscillatory and can be network pacemakers, motor patterns are often generated in a more distributed manner. Synaptic connections with other neurons are important because they either modify the rhythm of the pacemaker cell or are essential for pattern generation in the first place. Computational studies of half-center oscillators have made much progress in describing how neurons make transitions between active and inactive phases in these simple networks. In addition to characterizing phase transitions, recent studies have described the synaptic mechanisms that are important for the initiation and maintenance of activity in half-center oscillators. 相似文献
805.
Ultrastructural studies of the mouthparts of Musca domestica L. show that the fly's prestomal teeth are more damaging to host tissues than considered previously. When fed on tissue culture or pig cornea, SEM revealed that M. domestica were able to tear and suck up cells. This process occurs so rapidly, and so few cells are involved, that the damage is not perceptible to the naked eye. Except for the prestomal teeth, the mouthparts have few other structures which can inflict the damage observed. 相似文献
806.
807.
Masayoshi Tokita Win Chaeychomsri Jindawan Siruntawineti 《Evolution; international journal of organic evolution》2013,67(1):260-273
The tooth is a major component of the vertebrate feeding apparatus and plays a crucial role in species survival, thus subjecting tooth developmental programs to strong selective constraints. However, irrespective of their functional importance, teeth have been lost in multiple lineages of tetrapod vertebrates independently. To understand both the generality and the diversity of developmental mechanisms that cause tooth agenesis in tetrapods, we investigated expression patterns of a series of tooth developmental genes in the lower jaw of toothless turtles and compared them to that of toothed crocodiles and the chicken as a representative of toothless modern birds. In turtle embryos, we found impairment of Shh signaling in the oral epithelium and early‐stage arrest of odontoblast development caused by termination of Msx2 expression in the dental mesenchyme. Our data indicate that such changes underlie tooth agenesis in turtles and suggest that the mechanism that leads to early‐stage odontogenic arrest differs between birds and turtles. Our results demonstrate that the cellular and molecular mechanisms that regulate early‐stage arrest of tooth development are diverse in tetrapod lineages, and odontogenic developmental programs may respond to changes in upstream molecules similarly thereby evolving convergently with feeding morphology. 相似文献
808.
809.
Hugh H. Harris Stefan Vogt Harold Eastgate Peter A. Lay 《Journal of biological inorganic chemistry》2008,13(2):303-306
Quantitative X-ray fluorescence imaging of sections of human teeth revealed an increased concentration of copper and zinc
in carious regions of dentine compared with unaffected portions of the tooth. Higher-resolution images provided strong evidence
that the copper was transported and localized mainly in the dentinal tubules. While similar levels of zinc were found in these
areas and concentrated in the tubules, zinc was also more evident in the hydroxyapatite, and the increase in zinc levels compared
with the levels in background (normal) areas was less than that for copper. These results suggest a role for copper and zinc
in the formation and progression of dental caries and present a potential point of intervention for treatment.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Dedicated to the memory of the late Harold Eastgate. 相似文献
810.