Limulus polyphemus, is an excellent species for studies of intial sperm-egg interactions (Shoger and Brown, 1970). The gametes are easily obtained from mature animals, and fertilization and development can be demon- strated year around in the laboratory . Although the egg is comparatively large, quite opaque, and difficult to prepare for experiments involving embedding, much information on sperm-egg at- tachment is being obtained particularly with the use of frozen egg sections (Brown and Mowbray, in preparation) . However, as in many other species there is the necessity of observing fertilization in the whole egg . Thus, with the use of scanning electron microscopy, the study of gamete interac- tions, especially Limuluseggs and spermatozoa before and after their attachment, has been greatly enhanced . MATERIALS AND METHODS