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Principal Types (principal + type)
Selected AbstractsEyes and vision in Arion rufus and Deroceras agreste (Mollusca; Gastropoda; Pulmonata): What role does photoreception play in the orientation of these terrestrial slugs?ACTA ZOOLOGICA, Issue 2 2009Marina V. Zieger Abstract This paper deals with the orientational behaviour in the two terrestrial slugs Arion rufus and Deroceras agreste. It presents anatomical details of their eyes and provides an appraisal of the eyes' optical system. In both species the retinae contain two principal types of cell: photoreceptive and pigmented supportive cells. While only the eye of A. rufus apparently contains neurosecretory neurones, that of D. agreste is the only one equipped with a small additional retina with its own separate lens. Lens shapes vary between ovoid (A. rufus) and spherical (D. agreste). Our results demonstrate that the camera-type eyes in A. rufus and D. agreste have optical systems that do not allow the production of a sharp image on the retina. The slugs demonstrate negative visually mediated phototactic behaviour, but no polarization sensitivity. Only one aspect of the visual environment, namely the overall distribution of light and dark, seems to be important for these slugs. As the main role of the slugs' photoreceptors is to monitor environmental brightness and to assist the animal in orientating towards dark places, we conclude that these slugs do not need to perceive sharp images. [source] A new type of migrating zone boundary in electrophoresis: 1.ELECTROPHORESIS, Issue 2 2005General description of boundary behavior based on electromigration dispersion velocity profiles Abstract Till now two principal types of electrophoretic boundaries have been recognized: a steady-state one showing self-sharpening properties and an unsteady-state one showing electromigration dispersion (EMD). In this contribution, the existence of a third (hybrid) type of electrophoretic boundary is revealed, that shows simultaneously: (i) steady-state character with self-sharpening properties in a certain part of the boundary, demarcated by a certain range of its composition; (ii) unsteady-state character with EMD in the resting part. A new theoretical approach to the study of the structure and properties of electrophoretic boundaries is presented, based on EMD velocity profiles representing the dependence of the EMD velocity on the composition in any point of the transition region across the boundary. According to this approach, the linearity or nonlinearity of the EMD velocity profile is recommended as the criterion for distinguishing the actual type of the boundary in question. It is shown that the new type of electrophoretic boundary is not an exotic case but may be observed even in simple systems as, e.g., formed by adjacent zones containing mixtures of current species such as picrate and acetate. Computer simulations are presented which confirm the theoretical conclusions and illustrate the three types of electrophoretic boundaries. [source] Mixed-species bird flocks in dipterocarp forest of north-central Burma (Myanmar)IBIS, Issue 4 2001DAVID I. KING We studied the bird community in deciduous, dipterocarp forest of north-central Burma (Myanmar) during December 1994, March 1996, and January 1997 and 1999. Most members of this community participated in mixed-species flocks. Seventy-three flocks were encountered during our study, containing 52 species. Of these, 25 species occurred in more than 10% of flocks, and were included in our analyses. There were 26 significant correlations among species pairs, 25 of which were positive. Cluster analysis indicated that there were three principal types of flocks: one consisting mostly of small passerines and picids, commonly including Common Wood-Shrike, Small Minivet and White-browed Fantail, among others; a second type consisting mainly of sylviids, e.g. Arctic, Dusky and Radde's Warblers; and a third type which generally centred around Greater and Lesser Necklaced Laughingthrushes. Bird-eating hawks were numerous at these sites, and we witnessed several attacks on flocks during the study. Thus we infer that enhanced protection from predation is an important benefit conferred by flock membership. In contrast, there was little overlap in foraging behaviour among species, suggesting that foraging facilitation is a relatively minor benefit enjoyed by flock members, although we did observe White-browed Fantails and Greater Racket-tailed Drongos kleptoparasitizing other species on occasion. [source] Hepatic intraductal oncocytic papillary carcinomaCANCER, Issue 10 2002Robert C. G. Martin M.D. Abstract BACKGROUND There has been an increasing incidence and mortality from peripheral cholangiocarcinoma (PC) in the United States over the past 24 years. PC has been classified into two principal types, a mass-forming type and a periductal-infiltrating type, with a significant difference in the clinical behavior between the two. A third type, demonstrating a noninvasive intraductal growth of PC, was described as papillary PC. Rarely, papillary hepatic tumors composed of oncocytic cells have been described. Intraductal oncocytic papillary carcinomas (IOPCs) of the liver present as large, mucin-filled, cystic lesions lined by noninvasive or focally microinvasive oncocytic tumors. METHODS From June 1999 to August 2001, three patients with hepatic IOPCs were identified in the files of the Hepatobiliary Service, Department of Surgery, and the Department of Pathology at Memorial Sloan-Kettering Cancer Center. They form the basis of this study. We report the clinicopathologic presentation, as well as the outcome, with a review of the literature. RESULTS All three cases presented with well defined intrahepatic cystic masses ranging in size from 7.2 to 21.1 cm. The most prominent cells of the lining epithelium were columnar with oncocytic features showing abundant eosinophilic granular cytoplasm and centrally located nucleoli. All three patients underwent resection with one demonstrating local bile duct recurrence that was managed with stenting. Review of the literature has identified 39 patients with papillary PC and 2 patients with IOPC. The biology of these reported cases has been variable with overall survival better than that of nonpapillary PC patients, with recurrence in 15% of the reported cases. CONCLUSION Papillary PC is a rare type of cholangiocarcinoma that includes an interesting variant: IOPC. These tumors are predominantly found in men, who present with large (> 5 cm) mucinous cystic lesions of the bile duct. A noninvasive histology is seen, and long-term survival may be achieved with complete resection. Invasive variants of IOPC have been reported in the literature and have a worse overall prognosis. Cancer 2002;95:2180,7. © 2002 American Cancer Society. DOI 10.1002/cncr.10934 [source] | ||||||||||