Introduction

Abstract

Reptiles and birds are of substantial economic importance in egg and meat production for human consumption, as well as in the control of insects and rodent pests; among reptiles, turtles are receiving special attention with the aim of developing farms for turtle egg and meat production in some parts of the world. With the evolution of the amniotic (cleidoic) egg in reptiles, reproductive patterns became considerably modified in them. Turtles, crocodilians, and Sphenodon are oviparous, whereas the Squamata may be oviparous, ovoviviparous, or viviparous (Fitch 1970). Birds are exclusively oviparous (Gilbert 1979). Reptiles and birds have large eggs and greatly reduced fecundity. Because of their large size, the eggs of reptiles and birds are of great biological interest for the elucidation of the developmental and evolutionary processes involved in their growth and differentiation. Therefore, the developing ovarian follicles of reptiles and birds, which grow under the influence of gonadotrophic hormones to produce eggs and steroid hormones, were the subject of numerous studies in the past (see Loyez 1906, Brambell 1926, Callebaut 1975, Guraya 1976a, Dodd 1977, Jones 1978a, Gilbert 1979, see also Herpetologica, vol. 38, 1982). Actually follicle growth in the reptilian and avian ovaries is the result of complex processes of development and differentiation which involve (1) cellular and molecular changes of the nucleus or germinal vesicle; (2) structure, multiplication, chemical nature and function of various ooplasmic components of diverse morphology; (3) origin, structure and chemistry of yolk, including hormonal regulation of yolk synthesis, release and transport; (4) origin, chemical nature and function of various egg envelopes and their changing relationships with the growing oocyte. All of these aspects of growth of follicles or oocytes are closely accompanied by a series of complex cellular and molecular changes that lead to the formation of large egg cells in the ovaries of reptiles and birds.