Three-dimensional serial reconstruction of visual neuropils of left hemisphere in Achelia langi on basis of low-resolution image stack. A, three-dimensional reconstruction showing the arrangement and orientation of neuropils; posterior is up, dorsal is right. B, three selected sections showing original data for reconstruction; position of sections indicated in three-dimensional reconstruction top right. I , medium range of visual neuropil 1 (slice number 125); note two subsets of visual tract projecting through cell body rind, arrow indicating subset projecting to visual neuropil 1, arrowhead indicating subset projecting to visual neuropil 2. II, low range of visual neuropil 1 (slice number 376); note two subsets of visual tract projecting through cell body rind to visual neuropil 2 (arrowheads). III, beginning of visual neuropil 2 (slice number 640). Bar 10 μm. A, anterior; D, Dorsal; L, left; Np, neuropil; P, posterior; R, right; Th, thickening; V, ventral; VN1, visual neuropil 1; VN2, visual neuropil 2.