[Developmental capacities of fragmented labial gland anlagen of Formica pratensis (Hymenoptera)].

The imaginal labial gland ofFormica pratensis develops from three clearly distinguishable tissues of the larval gland: a) the common duct (UAG), including an epidermal part and the "Bulbus" region; b) the paired imaginai ring (IR); and c) the most anterior part of the paired duct (PAG), the so-called "apical cells" (AZ; see Fig. 1). Together these tissues represent the imaginal gland anlage. The larval common duct gives rise to the whole imaginal discharging system (consisting of a common and a paired duct). The imaginal reservoir is formed by the anterior cells of the imaginal ring, the size of which increases by cell multiplication. The posterior cells of the imaginal ring and the apical cells associate to form a so-called "agglomeration" which, after pupation, grows out to a system of glandular tubuli in such a manner that an apical cell is situated at the top of each tubule. - The developmental capacity of various fragments of the prepupal gland imaginal anlage was tested by implanting them into the body cavity of host prepupae of the same age. Within 1-14 days after transplantation the differentiated implants were studied histologically. - Development of transplanted complete imaginal gland anlagen corresponds to developmentin situ with two exceptions: 1. While differentiating into the imaginal discharging system, the larval UAG is lengthened only a little. 2. Instead of differentiating an imaginal salivarium, the epidermal tissue at the anterior end of the UAG closes to form a vesicle. - With the beginning of metamorphosis the imaginal anlage shows a mosaic determination and no regulation may occur: Though isolated, the three gland regions and parts of them develop according to their prospective significance. The size of the imaginal reservoir, for instance, depends on the number of available imaginai cells. - Differentiation of imaginai gland tubuli is possible only in presence of apical cells. One apical cell enables the surrounding imaginal cells to form one tubule; if the number of apical cells of an anlage is reduced, only less glandular tubuli are developed. - The apical cells show their tubuli forming effect only if they are in immediate cell contact to the imaginal cells; on the other hand it is not necessary for the tubuli forming cells to be in connection with the reservoir.