Neural Complex of Ascidians and Features of Its Structure in Polyclinidae

The structure of the neural complex has been studied under a light microscope in the representatives of 4 genera belonging to the family Polyclinidae. Particular attention was given to the relationships between the ciliary organ, dorsal tube, and neural gland. No dorsal string was found in Polyclinidae. The neural gland is located in the proximal portion of the mediodorsal blood vessel of the branchial sac. This paper discusses probable reasons for the differences in the structure of the neural complex in different ascidians taking into account original data and the existing literature.