By binding to sperm tails, SP prolongs the PMR. Thus, besides a carrier for genetic information, sperm is also the carrier for SP. Binding to sperm may protect the peptide from degradation by proteases in the hemolymph and, thus, prolong its half-life. Longer sperm tails may transfer more SP and thus increase the reproductive fitness of the male. We suggest that this could explain the excessive length of sperm tails in some Drosophila species.

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␤ -N-Acetylhexosaminidase, which is found almost ubiquitously in sperm of invertebrates and vertebrates, supposedly mediates a carbohydrate-based transient sperm-egg coat binding. In ascidians and mammals, ␤ -hexosaminidase released at fertilization from eggs has been proposed to modify sperm receptor glycoproteins of the egg envelope, thus setting up a block to polyspermy. Previously, it was shown that in potential sperm receptor glycoproteins of the ascidian Phallusia mammillata , N-acetylglucosamine is the prevailing glycoside residue and that the egg harbors three active molecular forms of ␤ -hexosaminidase. In the present study, P. mammillata ␤ -hexosaminidase cDNA was isolated from an ovarian cDNA library and characterized. The deduced amino acid sequence showed a high similarity with other known ␤ -hexosaminidases; however, P. mammillata ␤ -hexosaminidase had a unique potential N-glycosylation site. A phylogenetic analysis suggested that P. mammillata ␤ -hexosaminidase developed independently after having branched off from the common ancestor gene of the chordate enzyme before two isoforms of the mammalian enzyme appeared. In situ hybridization revealed stage-specific expression of ␤ -hexosaminidase mRNA during oogenesis in the oocyte and in the accessory test and follicle cells. This suggests that the three egg ␤ -hexosaminidase forms are specific for the oocyte, test cells and follicle cells.

Abstract.Asexual reproduction by formation of swimming buds which metamorphose directly into polyps plays a most important role in the propagation of Cassiopea andromeda (Cnidaria: Scyphozoa). (C. andromeda polyps, originally supplied by the LSbbecke Museum and Aquarium Dtisseldorf, FRG, were cultured in our laboratories.) We have defined five budding stages and investigated epithelial recruitment and dynamics during bud formation using intracellular vital stains. The region of cell recruitment was found to encircle the budding site asymmetrically. The aboral side contributing considerably less to the developing bud than the oral and lateral sides. Furthermore, it was found that the epithelial flow involved in bud formation is part of a permanent apico-basal displacement of ectodermal cells. Light and electronmicroscopic investigations revealed that no drastic changes occur at the cellular level, neither in the ectoderm nor in the endoderm which both participate in bud formation. Scanning and transmissionelectron microscopic investigations of the swimming bud revealed that the ectoderm is composed of three, and the endoderm of two, cell types. Nerve elements have been detected near the mesoglea between both ecto-and endodermal cells. Amoebocytes are regularly found either at the basis of epidermal cells or within the mesoglea, whereas symbionts are located in the endoderm. Buds induced to metamorphose by a bacterial-inducing factor were used to investigate morphological and ultrastructural changes occurring during metamorphosis and scyphistoma morphogenesis. Metamorphosis starts with the settling of a bud, followed by the formation of the pedal disk in which desmocytes, as typical cnidarian adhesive structures, are differentiated. Metamorphosis is completed with the formation of the mouth and tentacles. Whereas metamorphosis of cnidarian planulae implies considerable changes at the cellular level, tissue remodeling processes prevail in bud metamorphosis of C. andromeda.