Ultrastructure of the optic gland of the squid Sepiotheutis sepioidea (Cephalopoda : Loliginidae)

I describe the fine structure of the optic gland (OG) in the tropical squid Sepiotheutis sepioidea at different sexual maturity stages. Squids were co llected in Mochima National Park, Venezuela (10 degrees 20' 22 " - 10 degre es 24' N; 64 degrees 19' - 64 degrees 22' W). Morphometric characteristics and the development of reproductive organs at different sexual maturity sta ges (female n = 101; male n = 105), were significantly different (ANOVA, p < 0.001). The female gonadal index mean (GI = (ovary weight I body weight) x 100) between 0.1 - 2.95 %, and the male GI mean (GI = (testicule weight / body weight)x 100) oscillated between 0.22 - 1.38 %. The OG are a pa;ir of oval organs located at the posterior edge of the optic tract of the cephal opod brain. The OG showed the same cellular types described in other cephal opods, with slight differences. The secretory cells in young individuals pr esent a dendritic profile with thin cytoplasmic processes, numerous circula r mitochondriae with tubular crests and abundant ribosomes. At the last sta ge of maturity the secretory cells contain rough endoplasmic reticulum in t he form of dilated cisternae, with an active Golgi apparatus, secreting ele ctron dense granules. Mitochondriae are scarce and lipofuchsin granules sho w an increase in size. Secretory cell nucleus length and organelle abundanc e showed oscillations associated with the life cycle.