Abstract
Abstract: :
Purpose:Lymnaea stagnalis (Gastropod, pulmonate) is an animal model to study the associative learning. It responds to light with a withdrawal response after training. The unique geometry of the eye was described by Bovkova. To examine the structure of the retina, the Lymnaea eye were three dimensionally reconstructed. Methods:Pond snails were fixed with Bruin ’s fixative and the tissue including the eyes were embedded in paraffin. Serial sections (5µm in thickness) of the eye were stained with Hematoxylin and Eosin, and photographed. For reconstruction study, DELTAVIEWER was used. DELTAVIEWER is a computer program for three–dimensional reconstruction developed by Wada’s group, freeware for Apple Macintosh computers, and is available for download from http://vivaldi.ics.nara–wu.ac.jp/∼wada/DeltaViewer/. Results:The eyes are located at the medial side near the base of paired tentacles. Each eye is conical shape, measures 100µm in width and 120µm in length. Both eyes show symmetrical shape and position at 40–50 degree to the midline of the body symmetrically. The eye is closed vesicle, the anterior part is a cornea and the rest is a retina. A large spherical lens is located in the central portion in the ocular cavity. The retina is composed of 4 layers, a villous, pigmented, somatic and neural layer. The optic nerve extends from the posterior base. The analysis using DELTAVIEWER clarifies two depressions of both villous and pigmented layers in the retina. One is small and deep and another is wide and shallow. The villous layer faces to each other at these depressed areas. Conclusions:The Lymnaea eye shows a unique geometry of the retina. It is suggested that the depressed area differs from the rest area of the retina and may be more effective in the photoreception.
Keywords: photoreceptors • anatomy • retina