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 selfadministered 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. Anat Sci Educ 12:541-549.

This study aimed at examining the histological structure of the pecten oculi in the adult yellow‐legged gull, Larus michahellis, and at two moments of postnatal development: during the posthatch (nestling) and juvenile periods. Particular attention was paid to differences in the diameter of vessels, the thickness of the basement membrane, and ultrastructural features of endothelial and pigmented stromal cells. Capillary endothelial cells displayed numerous microvillous‐like folds projecting from their internal and external surfaces. Intercellular spaces between capillaries were occupied by pigmented stromal cells. The ultrastructure of pecten oculi underwent noticeable changes during postnatal development. The examination of the capillaries in nestlings, juveniles, and adults revealed that the formation process of vessels and pigmented stromal cells did not complete itself in the posthaching phase. The prominent feature of endothelial cells of capillaries in nestlings was that the microvilli were longer than in juvenile and adult cells, and the capillary lumen was therefore reduced. In this sense, their pigmented stromal cells showed fewer melanosomes, lacked intercellular spaces, and cellular junctions could still be observed. These results provide evidence that the pecten oculi during the posthatching phase maintains immature morphological features consistent with a role of pigmented stromal cells in the blood‐retina barrier.

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.

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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 morphological characteristics of the yellow‐legged gull's photoreceptors and cone distribution were studied using light and electron microscopy. In wholemount fresh retinas, five different coloured oil droplets located in the cone inner segments could be seen and characterized by colour, diameter and stratification. The photoreceptors were classified by comparing the fresh and fixed vertical sections under a light and electron microscope. Rods were easily distinguished from cones based on the outer segment morphology and the absence of oil droplets in their inner segments. Four types of single cones were associated with red, yellow, colourless and transparent oil droplets. Unequal double cones comprised a long principal member with a green oil droplet and an accessory short member containing a green microdroplet which was highly electron‐dense under electron microscopy. The different types of oil droplets were counted from microphotographs of fresh retinal samples in 20 regions. The density, percentage and diameter of the oil droplets were determined. The results showed that central regions had the highest oil droplet density which decreased towards the retinal periphery in all quadrants. Moreover, the oil droplet density was higher in the dorsotemporal quadrant than in other retinal regions. The average density of the red oil droplets was highest in the central areas, whereas colourless oil droplets had the highest density throughout the retina. In contrast, transparent oil droplets had the lowest density across all the regions of the retina. Finally, the retinal resolution was 52.61 cycles/degree. It was calculated using the posterior nodal distance and the oil droplet diameter. The work concludes by discussing the significance of the relative proportion of different cone types across the retina.

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