Zur morphologie des ventraltubus von Tomocerus-SPP (collembola: tomoceridae) unter besonderer berücksichtigung der muskulatur, der cuticularen strukturen und der ventralrinne

Abstract

The ventral tube of the Tomocerus spp. is an abdominal appendage. Microtubercles are arranged on its surface in different patterns. Their arrangement on surfaces, which are free from bristles and scales, is considered to reduce transpiration. All bristles are mechanoreceptors, but the scales are without sensory components. The ventral channel shows a tubular structure near the head and on the front side of the ventral tube. In the thoracic region, the channel is extended, and on tendon-plates it is even interrupted. For this reason, the ventral channel is considered to be unsuitable for transport of fluid. The division of the hemocoel in a frontal and a caudal cavity serves to facilitate hemolymph flow around the transporting cells in the tube vesicles. The fat body in the tube base also assists in the flow, possibly by contraction of the tube cylinder. Many excretory granules are accumulated in the fat body. The external formation of the ventral tube into basal plate, tube cylinder, tube flaps, and tube vesicles corresponds to the highly specialized and segmentated muscle system. There are 14 muscle pairs which are differentiated in proximal, lateral and distal muscles. The function of the proximal muscles is to move the tube cylinder and control its position, the lateral muscles move the tube flaps and support the erection of the tube cylinder, and the distal muscles retract the tube vesicles. The basal plate and tube cylinder can be homologized to the coxa. The structure that separates both parts serves, as in legs, as insertion for muscles, as do the basicosta and merocosta in higher insects. Embryologically, the ventral tube is considered to be a derivative of a real limb. Finally, the abdominal appendages with vesicles are discussed for all orders of Apterygota.