ABSTRACT
Oviducal glands (OG), also referred to as shell or nidamental glands (Prasad 1945, 1948; Knight eta/. 1993) are discrete, specialized regions of the anterior portion of the oviduct in cartilaginous fishes. Oviducal glands produce the components of the egg jelly that surrounds the fertilized egg in the early stages of embryogenesis. They also produce the tertiary egg envelopes including the rigid egg capsule of oviparous species, the thin pliable transient egg candle case of yolk sac species and the thin pleated egg envelope in most placental sharks (Hamlett et a/. 1998a, 1999; Hamlett and Koob 1999). OG have also been implicated in sperm storage (Metten 1939; Prasad 1945; Pratt 1993; Hamlett et a/. 2002a, b, 2003). Historically the terms shell, nidamental and oviducal gland have been used imprecisely and interchangeably. The region of the oviduct that produces a tough egg case that is deposited to the exterior in oviparous species is correctly termed the shell gland since this term denotes its function. A shell is defined as a hard, outer covering, hence the designation. The term nidamental gland is best used to refer to the gland that secretes the thin egg coverings of some viviparous species. The term nidamental is derived from nidus L. for nest. ln many placental species each embryo is surrounded by its own egg covering and the embryo and its coverings develop in its own uterine compartment, hence the nest. Neither of the
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previous terms can be correctly applied to the gland when referring to the region of the oviduct in some rays where no egg covering is produced. To establish a consistent terminology, we have chosen not to use the terms shell or nidamental but to use only the term OG to refer to any of the aforementioned glands since they are all derived from the oviduct.
