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The anatomical and histological features of the foveae in a gull, Larus michahellis, were investigated combining immunofluorescence and transmission electron microscopy. In an area of higher acuity, which extends in a band across the field of view, a central convexiclivate deep fovea was observed near of the pecten oculi. Moreover, a shallow fovea was present in the dorsonasal region. The central deep fovea was characterized by a remarkably and well-excavated pit containing extremely thin cones and a radial displacement of the cone axons and inner retinal layers. Immunofluorescence demonstrated the absence of rods and the presence of violet and green/red sensitive cone opsins. Ultrastructural analyses confirmed the lack of double cones, and specialized Müller cell processes forming a network that stabilizes the foveal structure. This deep central fovea, which provides the highest resolution and colour discrimination, may be used for monocular sideways vision of distant objects and a binocular fixation. The dorsonasal fovea was shallower and all retinal layers were present at the pit. This fovea showed the same composition of photoreceptors than central fovea and could be implied in magnification of a wide monocular part of the retinal image. The bifoveate condition of yellow-legged gull retina would allow the formation of three separate and distinct visual fields: two wide lateral monocular fields mediated by the dorsonasal and the central foveae, and a small binocular field mediated by the central deep fovea depending on ocular movements. This research was supported by the University of Alicante VIGROB-186.

The morphology of the retina of the adult Yellow-legged Gull, Larus michahellis, was examined in transverse sections under light microscopy in order to study the retinal adaptations to their specific photic environment that determines their behaviour. We identified rods, single cones and unequal double cones. Although it is a duplex retina, cones are preponderant and coloured oil droplets are present in their inner segments. As several colours in oil droplets are observed, it seems reasonable to conclude that several types of cones are present. Moreover, more cones per unit area are found in the central regions of the retina than in peripheral regions. A probable area centralis is observed. In the inner nuclear layer, two types of horizontal cells, and bipolar and amacrine cells can be recognised. Also, ganglion cells, characterised by prominent nuclei and nucleoli, vary in size and abundance among different regions in the retina. Comparisons are made with the retinae of other marine birds. The morphological characteristics of this retina indicate that Larus michahellis possesses: a good ability to discriminate colour; complex visual processing in the inner retina in order to mediate contrast and motion perception; and an elevated acuity in areas of high ganglion cell density.

The development of an effective program that combines in vitro maturation (IVM) and cryopreservation for immature oocytes would represent a novel advance for in vitro fertilization (IVF), especially as a means to preserve the fertility of women in unique situations. The aim of this study was to analyze the ultrastructural characteristics of human oocytes, obtained after controlled ovarian stimulation, to determine whether IVM is best performed before or after vitrification. To this end, we analyzed the following features in a total of 22 MII oocytes: size, zona pellucida and perivitelline space, mitochondria number, M-SER (mitochondria-smooth endoplasmic reticulum) aggregates and M-V (mitochondria-vesicle) complexes, the number of cortical granules and microvilli, and the presence of vacuolization using transmission electron microscopy (TEM). Each oocyte presented a rounded shape, with an intact oolemma, and was surrounded by a continuous zona pellucida and perivitelline space. Statistical analysis comparing oocytes vitrified before or after IVM indicated that there were no significant differences between examined characteristics.

The aim of this study was to provide a better understanding of the main difficulties hindering undergraduate biology students in learning histology. The study utilized a self‐administered questionnaire which included three closed‐ended and two open‐ended questions: (1) if students had difficulty in learning about each tissue type; (2) what might be the problem in learning about the tissue at hand; (3) which topics were the most difficult; (4) what were the possible reasons that made image identification of tissue types difficult; and (5) how to improve the course curriculum from a student perspective. The survey was administered to 139 undergraduate biology students enrolled in a histology course, of which 101 surveys were completed and analyzed both qualitatively and quantitatively. The topics that students experienced the most difficulties with were: nervous tissue, plant tissues, bone tissues, and glandular epithelial tissue. The main reasons students experienced difficulties with these tissue types, according to the students themselves, were the nature of the topic, grasping the terminology used, and insufficient teaching time. Students suggested the adoption of strategies such as: teaching based on practical tasks; reducing the content of the histology curriculum; adding anatomy subjects; and making histology education more interesting. This research was supported by the Teaching Program Networks from the Institute of Education Sciences at University of Alicante; Analysis of the difficulties in the learning of Histology Network (4146).