Influence of Vibrations on the Form of Sponge- Spicules. 573 



10. Herring, 'Archivf. d. ges. Physiol.,' vol. 107, p. 97 (1905); ibid., vol. 108, p. 267 



(1905). 



11. His, ' Arbeiten aus der Mediz. Klinik. Leipzig,' p. 14 (1893). 



12. Keith and Flack, ' Journ. of Physiol.,' vol. 41, p. 172 (1907). 



13. Kent, ' Journ. of Physiol.,' vol. 14, p. 233 (1893). 



14. Lewis and Oppenheimer, ' Heart,' vol. 2, p. 147 (1910). 



15. Lewis, Meakins and White, ' Heart,' vol. 5, p. 289 (1913-14). 



16. Lewis, White and Meakins, < Phil. Trans.,' vol. 205, p. 375 (1914). 



17. Lewis and Eothschild, ' Phil. Trans.,' vol. 206, p. 181 (1915). 



18. Lewis, 'Phil. Trans.,' vol. 207, p. 221 (1916). 



19. MacWilliam, ' Journ. of Physiol.,' vol. 9, p. 167 (1888). 



20. Eomanes, 1 Phil. Trans.,' vol. 166, p. 269 (1875). 



21. Sanderson and Page, 'Journ. of Physiol.,' vol. 2, p. 384 (1879-80); ibid., vol. 4, 



p. 347 (1883-84). 



22. Tawara, ' Das Eeizleitungssystem des Saugetierherzens,' Jena, 1906. 



23. Tigerstedt, ' Archiv f. Anat. u. Physiol.,' Phys. Abt., p. 497 (1884). 



24. Waller, ' Journ. of Physiol.,' vol. 8, p. 229 (1887). 



25. Wooldridge, ' Archiv f. Anat. u. Physiol.,' Phys. Abt., p. 522 (1883). 



26. Wybauw, ' Archiv Internat. d. Physiol.,' vol. 10, p. 78 (1910). 



On the Influence of Vibrations upon the Form of Certain Sponge- 



Spicules. 



By Arthur Dendy, D.Sc, F.RS., Professor of Zoology, and J. W. Nicholson, 

 M.A., D.Sc, F.R.S., Professor of Mathematics, in the University of 

 London (King's College). 



(Received May 11, 1917.) 



It has been pointed out recently* by one of us that the development of the 

 remarkable chessman-spicule or discorhabd in the genus Latrunculia is a 

 somewhat complicated process depending upon several factors. The proto- 

 rhabd or axial thread appears first as a slender rod capable of independent 

 growth. With these protorhabds two kinds of silica-secreting cells appear to 

 be' associated, viz., formative cells which are responsible for the actual 

 deposition of the silica upon the protorhabd, and accessory silicoblasts which 

 are supposed to collect supplies of silica and bring them to the formative 

 cells to be used in the process of spicule-formation. The spicule in this case 

 consists of an elongated axis with whorls of flattened lobes arranged at more 

 or less definite intervals along its length, and it was suggested that the 



* A. Dendy, Presidential Address to the Quekett Microscopical Club, 'Journ. Q.M.C., 

 Ser. II, vol. 13, p. 231 (1917). 



