The Structure of the Gonads, Gametogenesis, and Sperm-Egg Interactions in the Anthozoa

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Abstract
In the Anthozoans Metridium sp. and Bunodosoma cavernata the testes are located in the secondary septa. The cysts of the testis are surrounded by mesoglea. Bounding the mesoglea on each side of the septa is the gastrodermis. The gastrodermal cells exhibit interesting flagellar specializations. Each cell has a flagellum which extends into the gastrovascular cavity and is surrounded by long microvillus-like extensions. It is suggested that these specializations may serve in a sensory capacity. The periphery of the testicular cysts contains the early spermatogenic stages, while spermatids and sperm are more centrally located. In both Metridium sp. and B. cavernata the early spermatids are connected by intercellular bridges. These spermatids exhibit early flagellar formation. The distal centrioles have two associated specializations, satellites and pericentriolar processes. During spermiogenesis there is a general polarization of the cytoplasm and several maturational events occur more or less simultaneously. Nuclear condensation begins, mitochondria aggregate and fuse, and lipid-like inclusions associate with this mitochondrial complex. Concave or “donut” shaped vesicles are noted in association with Golgi complexes. The sperm of both species contain electron dense nuclei, lack distinct acrosomes but have vesicles associated with the lateral sides of their heads between the nuclear envelopes and plasma membranes. In both sperm, lipid-like inclusions are associated with complex mitochondrial bodies. The sperm of Metridium exhibit an interesting membrane response when exposed to eggs. The plasma membrane along the side of the head of the sperm sends out long finger-like protrusions. The eggs of both Metridium sp. and B. cavernata exhibit cortical reactions. In Metridium the dehisced cortical substance appears to be lost to the environment, while in B. cavernata it forms a flocculent coat around the egg.

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