Rve Cord of the Ly Resembles That

behaviour. W chemical ch not known, the neurona providing ev of aspects o 1991; Paul, needed, however, because although circuits and their components do change, it is not yet clear which features are relatively well conserved and which are modified. One difficulty of using the comparative method in an evolutionary context is deriving an acceptable representation of the primitive condition by evaluating a number of related, but differently evolved, modern species. We are testing a novel approach to this problem, open to us because Australia has a relict population of the syncarid crustacean Anaspides tasmaniae. Fossil and morphological evidence from extant syncarids suggests that they have altered little in their external morphology for at least 300 million years (Schram, 1983) and probably represent a form close to the ancestral malacostracan condition. If constancy in external morphology is mirrored by a similar stability in the nervous system, a likely but unproved may strac pro us sy nform ary as use g bo behaviour and the structure and function of its nervous system (e.g. Macmillan and Field, 1994; Pasztor and Macmillan, 1990; Sandeman et al. 1988, 1993). Here we report on a comparison of serotonergic immunoreactivity in the neurones of the anterior nerve cord of Anaspides tasmaniae and Cherax destructor.