الفهرس 
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Abstract
Key words: Branchiostoma, testis, ovary
Cephalochordates – commonly known as “Lancelets” – are the key to understanding the vertebrate origins, hence comes the importance of this study. Branchiostoma lanceolatum (Amphioxus) specimens were collected monthly – with the exception of few months – from the Red Sea shores near Fayed region. These specimens were submitted to morphological, histological, and ultrastructural investigations. Researches on B. lanceolatum had never been carried out before in this locality.
The present study reports that spawning of this animal occurs all over the year, and its highest values were encountered in summer. Therefore, the present study suggests that the breeding period extends all over the year instead of only few months as was suggested before. The present study also states that the spermatogenic epithelium follows the basic pattern of all vertebrates: spermatogonia – with two forms “A” and “B” – divide to give spermatocytes; which in turn divide to give spermatids that undergo morphological transformations to produce spermatozoa at the end. The ovary of such magnificent animal has three developmental stages: the previtellogenic (immature) stage, the vitellogenic stage, and the mature stage. The ovary is lined externally with a layer of germinal and non-germinal cells. The germinal epithelium comprises oogonia and oocytes. Three stages of the oocyte can be seen. Stage one: which is the smaller-growth-stage oocyte; stage two: this is the medium-growth-stage oocyte; and stage three: which is the large-growth-stage oocyte. Each of these is responsible for a different metabolic process. Non-germinal follicular cells can be found in the form of flattened cells with tapering ends, adherent to the outer surface of the oocytes as they grow. The histological and ultrastructural studies were conducted in the summer season when the gonads are full and ripe.