General Considerations

Abstract

In contrast to most vertebrates, which discharge semen in a fluid state, that is, as suspensions of free spermatozoa in seminal plasma, in many invertebrates, but only a very few vertebrates, the spermatozoa undergo aggregation into all sorts of conglomerates or packages, some loosely, others tightly wrapped, before they are passed on to the females. In most instances the wrappers consist of male accessory secretions which in the course of enfolding the spermatozoa have undergone gelation, coagulation or similar forms of hardening and solidification. The resulting sperm-encompassing devices can range in appearance from simple, un-differentiated mucous coats to structurally complex, multilayered, often tough and highly elastic tunics or capsules.