On some variations in the latero-sensory lines of the placoderm fish Bothriolepis

Abstract

Some variations of the superficial latero-sensory lines of the antiarch fish Bothriolepis are described. These are considered to be due to the sensory lines having become anchored to different combinations of bone rudiments at an early stage in skeletogenesis; during later growth they were consequently drawn along different courses. Some effects of the tensions involved in this process are considered. Loose ends of sensory lines extending beyond their normal points of anchorage are regarded as important, partly because they themselves may become sites of further anchorages and partly because they may form unions with other sensory lines. A similar approach is applied to some problems in arthrodires. The central sensory line of Bothriolepis may be derived from a posterior pit-line of the normal arthrodire type as a result of a transference of anchorage at both its ends. In another kind of variation in Bothriolepis a sensory line appears to have channelled the growth of advancing horizontal bone lamellae in such a way that the suture formed between adjacent bones becomes coincident with the sensory line for a short part of its course.