1Any of a series of openings between the gill arches of a fish, through which water passes from the pharynx to the exterior, bathing the gills in the process.
- ‘They have long ugly snouts and gill slits which seem almost to encircle the whole head.’
- ‘Water is taken in through the spiracles, passed over the gills, and expelled through the gill slits on the underside of the body.’
- ‘Water exits through the gill slits at the back of the head.’
- ‘One small gill slit is found in front of each pectoral fin.’
- ‘Adults are uniformly brownish gray, shiny on top and pale on the ventral side and around gill slits.’
2A set of grooves similar to gill slits found in embryos of higher vertebrates.
- ‘For Darwin, such apparently useless phenomena as the human appendix, or the tail and gill slits of the early stages of the human embryo, were signs of our evolutionary history.’
- ‘Although they retain the chordate characters as adults gill slits are present only in the embryonic stages of land vertebrates.’
- ‘Another myth is the claim human embryos go through a fish-like stage and display gill slits.’
- ‘This may be illustrated by the gill slits in the embryos of higher vertebrates like reptiles, birds and mammals.’
- ‘Thus, the gill slits of the early human embryo supposedly repeat our distant ancestral past as a fish, while the transient embryonic tail, developing just afterward, marks the later reptilian phase of our evolutionary ascent.’