558 Notes. 



\\\ the Latter group, the "index of extinction" gradually 

 increases from the first element to the last; thus : — 



index of extinction. 



Epithelial cilia .. .. .. .. .. 1*51 



Cilia of Protozoa .. .. .. .. .. 1*51 



Swimming-plates of Ctenophora . . . . 1 • 53 



Flagella 1-56 



Bibliography. 



Borrel & Cernovodeanu — Membrane ondulante de Spirochasta balbianii. 



C.E. Soc. Biol. Paris, xlii. (1907) p. 1102 (1 fig.). 

 Engelmann — Kontraktilitat u. Doppelbrechung. Arch. f. Ges. Physiol, xi. 



(1875) p. 432. 

 Fantham — Spirochasta (Trypanosoma) balbianii and Spirochmta anodontm. 



Quart. Journ. Mier. Sci., lii. (11)08) pp. 1-73 (3 pis ). 

 Rouget — Sur les phehomenes de polarisation qui s'ohservent dans quelques 



tissus. Journ de Physiol. (Brown-Sequard) v. (1862) p. 2-17 (1 pi.). 

 Vles — Structure et affinity's de Trypanosoma balbianii. C.E. Soc. Biol. 

 Paris, hi. (1906) p. 408 (1 fig.). 

 „ Sur la birefringence apparente des cils vibratiles. Comptes Bendus, 

 cxlvi. (1908), pp. 88-9. 



