Introduction

Shell-less culture of embryos is a technique which involves culturing embryos with associated yolk and albumen outside of the eggshell and shell membranes. In contrast to shell windowing techniques, shell-less culture allows continuous observation of, and access to developing embryos and extra-embryonic membranes almost to the time of hatching. Injections can be made into, or operations performed on, a specific portion of the embryo, and resultant changes in heart rate, behaviour, regional growth or other parameters observed continuously without having to sacrifice the embryo. Due to lack of adhesion of extra-embryonic membranes to an overlying shell window, multiple injections or operations can be performed on a given embryo in shell-less culture. Additionally, grafts consisting of embryonic, neoplastic or other tissue onto the chorio-allantoic membrane of a single embryo can be followed routinely without having to sacrifice either host or graft tissue. Of particular interest, avian embryos maintained in shell-less culture become calcium-deficient due to the absence of the eggshell (Dunn & Boone, 1977; Tuan, 1980, 1983; Richards, 1982; Ono & Wakasugi, 1984). Thus, shell-less culture provides a unique experimental system for studying the relationships between calcium homeostasis and other metabolic and physiological functions during development (Tuan et al., Chapter 27). In the past, investigators have cultured avian embryos in a variety of vessels including: glass dishes (Assheton, 1896; Fere, 1900; Loisel, 1900; Paton, 1911; Vogelaar & van den Boogert, 1925; Vollmar, 1935; Schmidt, 1937), ceramic dishes (Corner & Richter, 1973), beakers (Romanoff, 1943; Boone, 1963; Palen & Thorneby, 1976) evaporating dishes (DeGennaro et al, 1980), plastic shells (Quisenberry & Dillon, 1962), petri dishes (Williams & Boone, 1961), sandwich bags (Schlesinger, 1966; Elliot & Bennet, 1971), and in sandwich-type plastic wrap in several configurations (Criley, 1971; Dunn, 1974) with varying degrees of success.