1. 1. Land, M. F. /. exp. Biol. 51, 433–470 (1969). 2. Land, M. F. J. exp. Biol. 51, 471–493 (1969). 3. Blest, A. D. The Neurobiology of Arachnids (ed. Barth, F. G.) 79–102 (Springer, Berlin, 1985). 4. Williams, D. S. & Mclntyre, P. Nature 288, 578–580 (1980). 5. Blest, A. D., Hardie, R. C, Mclntyre, P. & Williams, D. S. /. comp. Physiol A 145,227–239 (1981). 6. Jackson, R. R. & Blest, A. D. /. exp. Biol. 97, 441–445 (1982). 7. Wanless, F. R. Bull. Brit. Mus. not. Hist. Zool. 46, 135–205 (1984). 8. Blest, A. D. & Sigmund, C. Proc. R. Soc. B 221, 111–125 (1984). 9. Blest, A. D. & Sigmund, C. Protoplasma 125, 129–139 (1985). 10. Blest, A. D. & Price, G. D. Protoplasma 120, 172–184 (1984). 11. Blest, A. D. /. comp.,Physiol. A 157, 391–404 (1985). 12. Homann, H. Z. Morph. Tiere 69, 201–272 (1971). 13. De Beer, G. R. Embryos and Ancestors 3rd edn (Oxford University Press, 1958). 14. Blest, A. D. Phil Trans. R. Soc. B (in the press). 15. Blest, A. D. & Carter, M. Phil. Trans. R. Soc. B (in the press). 16. Eakin, R. M. & Brandenburger, J. J. Ultrastruct. Res. 37, 618–663 (1971). 17. Jackson, R. R. & Blest, A. D. /. Zoo/. Land. 196, 255–293 (1982). 18. De Voe, R. D. / gen. Physiol. 66, 193–208 (1975). 19. Yamashita, S. & Tateda, H. / comp. Physiol. A 105, 29–41 (1978). 20. Yamashita, S. & Tateda, H. J. exp. Bio/. 74, 47–58 (1978). 21. Uehara, A., Toh, Y. & Tateda, H. Cell Tiss. Res. 182, 81–91 (1977). 22. Blest, A. D., Mclntyre, P. & Carter, M. J. comp. Physiol. (in the press).